The climate of the Valley of Mexico ranges from a semi-arid zone in the north to a tropical zone in the south. The valley has annual rainfall of 700 millimeters (27.6 in), which is concentrated in the months of June to September/October and during the rest of the year there is little or no rainfall. Today, there are hardly any permanent rivers; Therefore, groundwater is the main water resource of the valley.

The valley does not have any natural drainage outlet for water coming from the slopes, which makes the city vulnerable to flooding. This was opened artificially through the use of canals and tunnels (work began in the 19th century) and what used to be Lake Texcoco was completely drained.

The rural southern part of the Federal District and the Valley of Mexico, especially the Chichinautzin mountain range, is the most important natural recharge zone for the Mexico City aquifer due to the relatively high levels of precipitation and the high permeability of its basalt.[1]​.

Management of water resources. The National Water Commission (CONAGUA) is responsible for the management of water resources in Mexico, including the granting of water extraction and wastewater discharge permits.

Water supply and sanitation. The National Water Commission also supplies water in large quantities to the Federal District and parts of the State of Mexico through the Cutzamala and Lerma systems.

In the State of Mexico, the State Water Commission purchases bulk water from CONAGUA, transmits it through its own bulk water infrastructure, and sells it to 57 municipalities, with 4.1 million inhabitants. The State Water Commission also monitors water quality, provides technical assistance to municipalities for water disinfection and sewer cleaning, operates wastewater pumping stations and five wastewater treatment plants, empties septic tanks, and supplies water by tanker trucks in emergency situations. It also provides training and assistance to municipalities in the establishment of municipal public services (operating organizations).[2] Each of the 59 municipalities of the State of Mexico and the municipality of the State of Hidalgo that are part of the Metropolitan Zone of the Valley of Mexico are responsible for water supply and sanitation.

Mexico City's municipal public water supply service, Sistema de Aguas de la Ciudad de México (SACM), is responsible for water supply and sanitation in the Federal District. Its director is appointed by the district government.

Contenido

La infraestructura hídrica de la Zona Metropolitana del Valle de México está formada por infraestructura para el abastecimiento de agua en grandes cantidades y la distribución de agua (abastecimiento de agua), la recolección de aguas residuales, la recolección de aguas pluviales y el tratamiento de aguas residuales (saneamiento), y el riego principalmente con aguas residuales.

Water supply

The Federal District and the State of Mexico together had 1,089 registered wells with a depth of 70 to 200 meters in 1994. These do not include the wells commissioned by the National Water Commission, which are deeper. There are also a large number of unregistered wells, many of which are located in the State of Mexico. Generally, the wells are located in four different well fields. These are labeled as Southern (or Xochimilco), Metropolitan, Eastern (or Texcoco region), and Northern well fields.[1]​.

Apart from these well fields, Mexico City's bulk water supply infrastructure is made up of two systems: Lerma and Cutzamala. The Lerma system, built in the 1940s, transfers 4.8 m/s of water (6% of the total water supply for the Metropolitan Zone of the Valley of Mexico) from well fields in the upper basin of the Lerma River west of Mexico City. The Cutzamala system was built in stages from the late 1970s to the late 1990s to transfer 14.9 m/s (19% of the total supply) of water from the Cutzamala River in the Balsas basin, southwest of the Metropolitan Area of ​​Mexico City, for use as drinking water, for which it was raised more than 1,000 meters. It uses 7 ponds, a 127 km long aqueduct with 21 km of tunnels, 7.5 km of open canals and a water treatment plant. Its cost was US$1.3 billion.[3]​ Although it provides Mexico City with more than 20% of its water, the Cutzamala system currently operates at only 47% of its total capacity.[4]​ Both systems are launched by the National Water Commission.

The Federal District's water distribution system incorporated almost 11,000 kilometers of distribution lines and 243 storage tanks with a capacity of 1.5 million cubic meters in 1994. Water from different sources is added to common distribution systems. The Federal District has also put into operation a water transmission line (the Peripheral Aqueduct) that transports water from the Cutzamala system (entering the distribution system from the west) to the southwestern and eastern part of the district. The State of Mexico system has almost 800 kilometers of distribution lines and 32 storage tanks with a capacity of 440,000 cubic meters. The State of Mexico puts into operation the 49 kilometers of water distribution lines (the Macrocircuit) to transport water from the west side of the service area (including water imported from the Cutzamala-Lerma system) to the east side. This transmission line is being upgraded to increase the volume of water taken from the Cutzamala-Lerma system to 7.3 cm and provide service to the eastern area. The State Water Commission puts the Macrocircuit into service.[1]​.

Combined sewer system

The Valley of Mexico Metropolitan Area is served by a unified combined sewer system that collects municipal wastewater, industrial wastewater, and stormwater. This includes 11.8 km (7.4 miles) of pipelines,[5]​ 68 pumping stations, numerous dams, lagoons, and flow control reservoirs, 111 kilometers of open canals, 42 kilometers of rivers used primarily for drainage, and 118 kilometers of tunnels and underground collectors (interceptors and emitters).[1]​ The three interceptors are as follows:.

• - The western interceptor (Interceptor del Poniente) flows into the Nochistongo channel, which finally joins the central emitter;.

• - The Central Interceptor flows into the Central Emitter (Deep Drainage) and then into the Salto River of the State of Hidalgo, near the Requena Dam, from where it flows to the Mezquital Valley; and.

• - The eastern interceptor (Interceptor del Oriente) empties into the Grand Canal, then passes through the old and new tunnels of Tequixquiac and, finally, empties into the Salado River.[6]​.

The total low flow rate of the Valley of Mexico Metropolitan Area, which is primarily composed of untreated municipal wastewater, was estimated at 44 m/s in 1993. During the rainy season, the region experiences many high-intensity, short-duration storms. A single storm can produce up to 70 millimeters (about 3 inches) of precipitation, which represents about 10 percent of the total annual precipitation. Taking this rainfall pattern into account, the overall drainage system was designed to transport 200 m/s over a 45-hour period.

Until 1910, the Grand Canal operated purely by gravity with an inclination of 19 cm per km. Over the next five decades, its inclination was reduced to 10 cm per km due to land subsidence of 7 meters. Some large pumps were installed in an attempt to maintain its capacity.[6]​[7]​ After the major floods of 1950 and 1951, it became clear that the Grand Canal could no longer protect the city against flooding and the creation of a deep drainage system was proposed for the first time. In 1959 studies on the system began; Its construction began in 1967 and was completed in 1975. It consists of a deep tunnel, the Central Emitter, with a length of 68 km and a depth of up to 250 m. Today it constitutes by far the most important element of Mexico City's drainage system. The system was designed for a flow of 170 m/s. However, due to additional land settlement, the inclination of the Grand Canal became zero in 1990 and negative in 2000. Despite the installation of additional pumps, the capacity of the Grand Canal decreased from 80 m/s in 1975 to 15 m/s in 2008. This in turn affected the Central Emitter, which had been designed to be closed during the dry season for maintenance. Due to the settlement of the Grand Canal, the continually filled with water, making it impossible to inspect it for problems or maintain it, so maintenance could not be carried out between 1995 and 2008. The tunnel has deteriorated due to excess loading and corrosion of its 65.62m (20 ft) diameter walls[5]​ and its capacity has been reduced to 120 m/s. In 2008, it underwent maintenance for the first time in more than 12 years.

Reuse for other purposes

Water reuse activities in the Valley of Mexico Metropolitan Area officially began in 1984 under the national program for efficient water use, including the recharge of aquifers with stormwater and reclaimed municipal wastewater, as well as the use of reclaimed wastewater in the industrial and service sectors. This national program included the creation of new wastewater discharge regulations by the Federal District and, in 1990, provisions were established for an industrial pretreatment program, an important prerequisite for any reclamation and reuse activity. However, little information is available on the extent and success of industrial pretreatment programs.

Within the service area of ​​the Federal District, the 2.62 m/s of reused treated wastewater is distributed as follows:

• - 83 percent for the irrigation of urban gardens and recreational reservoirs.

• - 10 percent for industrial uses.

• - 5 percent for agricultural irrigation, and.

• - 2 percent for commercial uses such as car washing.

Industries recycle and reuse wastewater generated by themselves or municipalities. For example, 26 private companies in the Vallejo area began a reuse program in 1989 with the establishment of a for-profit company: Aguas Industriales de Vallejo. The company rehabilitated a former municipal wastewater treatment plant and began distributing reclaimed water to its shareholder companies at three-quarters the cost of government-supplied drinking water.

A major wastewater reclamation and reuse project exists at Lake Texcoco along with other flood control and dust removal programs. Between floods, the lake's shallow saline bottom could dry out and produce strong dust storms. In response to this problem, the Texcoco plan was established in 1971. The solution was to create smaller permanent ponds within the extensive, intermittent lake bottom and rehabilitate problem areas for further urban and agricultural expansion through windbreaks, revegetation, agricultural irrigation and drainage improvements. Artificial and more permanent lakes were created by applying the knowledge obtained from the problem of subsidence. High pumping rates allowed the clays to consolidate and the former lake bottom to drop by about 4 meters in places. The reuse component of Texcoco's plans includes the construction of a wastewater treatment system through a facultative lagoon and the reclamation of rainwater collected for agricultural irrigation. Therefore, the drinking water currently used for this purpose will be replaced.

The Federal District built two pilot treatment plants in 1983 in order to study their potential for advanced treatment of secondary effluent wastewater for potable reuse and to analyze the potential to treat contaminated groundwater. Based on the results of the experimental treatment plants, new treatment facilities with a capacity of 0.3 m/s were built and designed for groundwater treatment and direct potable reuse. The stated goal of the reuse project was to mix reclaimed wastewater with treated groundwater and introduce the mixture directly into the distribution system. Currently, reclaimed wastewater is being used for non-potable purposes.[1]​.

Artificial groundwater recharge

Artificial groundwater recharge is currently being carried out in the Metropolitan Zone of the Valley of Mexico using flood water and treated wastewater.

Artificial flood water recharge has been carried out in the area since 1943 as a method of flood mitigation rather than as a method of groundwater recharge. Initial projects involved surface runoff retention and dispersion, channel modifications, and infiltration wells. Many of these projects were carried out in the highly permeable basalt of the highlands and very high infiltration rates were achieved during periods of heavy rainfall. Artificial flood water recharge using injection wells was first developed in the Federal District around 1953. However, half of the wells were subsequently closed due to operational problems. In 1970, a series of approximately 56 wells were developed for the purpose of stormwater disposal. These wells together could contain up to 35 m/s of water. Although the wells were not designed for recharge purposes, stormwater likely reached the aquifer.

The Texcoco project mentioned above has carried out studies on the indirect potable reuse of reclaimed wastewater through artificial recharge of the aquifer using secondary and advanced municipal wastewater treatment. The final effluent can be used in infiltration ponds or injection wells. In an independent program carried out by the Federal District, a pilot plant injected water treated with advanced processes directly into the aquifer at a rate of up to 0.05 m/s. Monitoring wells were used to evaluate changes in water quality and pressure levels.[1]​.

Entre estos, se incluyen la sobreexplotación de agua subterránea, el hundimiento de tierra, el riesgo de grandes inundaciones, el impacto de la creciente urbanización, la baja calidad del agua y el suministro intermitente, el uso ineficiente del agua, un índice bajo de tratamiento de aguas residuales, problemas de sanidad sobre la reutilización de aguas residuales para riego y la recuperación limitada de costos para el agua. La cobertura de la infraestructura en términos de acceso a una conexión de conductos de agua o al saneamiento, la cual se utiliza para supervisar los Objetivos de Desarrollo del Milenio para el abastecimiento de agua y el saneamiento, es casi universal en la Zona Metropolitana del Valle de México y como tal no constituye un reto.

Overexploitation of groundwater

The exponential growth of the population of the Mexico City Metropolitan Area has depleted its groundwater resources. The recharge of the aquifer is about 31.6 m/s which, when compared to the extraction of 59.5 m/s, results in an excess consumption of 28 m/s.[10]​ In 1983, systematic monitoring of the aquifer's water levels began. Since that time, the average annual decline in groundwater levels varies from 0.1 to 1.5 meters per year in different areas. Taking into account the current rate of depletion, the estimated storage volume has been calculated to be between 200 and 350 times the annual extraction. However, with a simplistic approach to the water balance, other realities are being ignored. For example, the aquifer is vulnerable to geologically induced water quality problems with increasing aquifer consolidation and depth and fragmentation of clay layers. Furthermore, it is possible that the actual available volume of the main aquifer was less than estimated due to the probable reduction in porosity with increasing depth. There are also practical and economic limitations to the pumping depth.[11]​.

What follows is the water balance of the Metropolitan Zone of the Valley of Mexico:

land subsidence

The city rests on the highly saturated clay of ancient Lake Texcoco. This soft foundation is collapsing due to over-extraction of groundwater. Land subsidence in Mexico City caused by overexploitation of groundwater over the last hundred years has been up to 9 meters and, as a consequence, damage has occurred to buildings, streets, sidewalks, sewers, stormwater drains and other infrastructure.

Flood

Flooding is common in Mexico City and swamps roads and sidewalks. In low-lying neighborhoods like Iztapalapa, residents are so accustomed to seeing a fetid sea of ​​sewage rising in the streets that they have built small dams in front of their houses.[5] Floods are caused by the joint subsidence and increased impermeability of the soil due to urbanization. According to the modeling, if the Central Emitter failed during the rainy season, a major flood would occur that would flood the historic center, the Mexico City International Airport, and the eastern districts of Mexico City.[12]​.

Increase in urbanization

Urban growth reduces soil permeability in groundwater recharge zones and increases the risk of flooding. It is estimated that the metropolitan area grows annually from 200 to 300 hectares in the recharge areas. For every square meter that is built, an average of 170 liters of recharge is lost per year. In this way, for every hectare that is built, water is lost for 500 families and the groundwater pressure additionally increases.[13] Between 1989 and 1994, the Federal District declared six environmental protection zones, mainly in forests and hillsides, with a total area of ​​almost 5,000 hectares in order to protect them from urbanization.[14]​.

Water quality and intermittent supply

Poor water quality is a concern at the source and point of use. Initially, it was believed that Mexico City's groundwater was protected from contamination by a thick impermeable layer. However, this layer has been fragmented due to land subsidence. Likewise, the natural upward flow of water in the Artesian Well has now been reversed due to groundwater depletion. In this way, it is believed that Mexico City's groundwater will become increasingly vulnerable to contaminants from landfills and industrial sites that leach into the aquifer. In addition, the deep drainage system penetrates the clay (aquitard) in some places of the main aquifer. During periods of heavy rain, wastewater leaks out of the deep tunnels into the surrounding subsoil and causes contamination of the aquifer.[15]​.

Distribution system leaks are a major concern for drinking water quality. When wastewater enters the ground from leaking sewers or other sources, when the pressure is low the leaking pipes become infiltrated with contaminated water. According to the Federal District Water Quality Laboratory, neighborhoods that experience more frequent service interruptions have worse quality water than neighborhoods with constant supply. The percentage of household tap water samples in compliance with the residual chlorine standard (0.2 milligrams/liter) was 87 to 100 percent of the tests carried out in 1993 and was notably low in the southeastern delegations (Iztapalapa, Tláhuac and Xochimilco). Household water storage tanks or tinacos are common on almost all house roofs and usually store water when the system's water pressure is inadequate. In many cases, the tanks are open and not cleaned regularly, which causes residual chlorine to dissipate and encourage the growth of microorganisms. The standard levels of chlorine (0.2 milligrams/liter) maintained in the distribution system upon reaching the customer's tap are not sufficient to eliminate microorganisms that may have penetrated the pipes.[15]​.

The water supply in many parts of the Metropolitan Area of ​​the Valley of Mexico is intermittent and the pressure is usually insufficient. Thus, users have to supplement their water supply with water purchased from tanker trucks or pipes. Occasionally, the water supply is even interrupted for several days, as happened in January 2009 when the Cutzamala system's water supply had to be reduced, cutting off water to 5.5 million people for three days.[16] This incident was followed by a second supply interruption in March 2009 and, more recently, a third interruption in April 2009. This third interruption was made in response to the alarmingly low levels of the city's water reserves. and carrying out repairs in the Cutzamala system. This lasted 36 hours and left more than five million city residents without water services. In response, the Mexico City government has had to implement an emergency supply response program, whereby water is provided in tanker trucks and bottles to residents of affected communities.[4]​.

Limited wastewater treatment and concerns about reuse for irrigation

As mentioned previously, only 15% of the wastewater in the Metropolitan Area of ​​the Valley of Mexico currently receives treatment. Stormwater, raw municipal wastewater and partially treated industrial wastewater are mixed together and reused for large-scale irrigation.

There are concerns about the health and environmental impact of reusing raw wastewater from Mexico City for irrigation. Crops grown with wastewater are limited to crops that are not eaten raw, but these limitations are difficult to enforce and farmers also grow vegetables using wastewater. According to a study by the International Water Management Institute (IWMI), these risks must be carefully considered, but the importance of this practice for the livelihoods of countless smallholders must also be taken into account.[17]​ Studies on soils irrigated with untreated wastewater for 50 years reveal an accumulation of heavy metals in the soil, but also that they accumulate to a lesser extent in plants.[18]​ According to another study, bacterial contamination has been found in the water of the canals used for bathing and in the groundwater used to supply drinking water from irrigated areas where wastewater has been reused, which has led to a high incidence of diarrhea and skin irritations.[19]​.

Inefficiency in urban water use

The Federal District has a non-profitable water level of 40%, close to the national average, which implies that only 60% of the water pumped into the system is actually billed. A large percentage of unprofitable water is not due to leaks, but to illegal connections. Additionally, SACM, the district's water department, has by far the lowest collection efficiency among the top 25 municipalities, only receiving payment for 40% of all its bills. Therefore, only 24% (60% billed, 40% bills paid) of the water pumped into the system is paid for. The level of non-profitable water in the State of Mexico is lower, so that the average level of the metropolitan area is 36%.

Figures regarding per capita water use are difficult to compare over time, as sources typically do not indicate whether water losses are included in the figures or not. The National Institute of Statistics and Geography established the Federal District's water use at 223 liters/day in 1999 (probably after losses), including 164 liters for residential use and 59 liters for industrial and commercial uses. This is only one-third of the average US water use, which is 603 liters/person/day. However, it is still a third higher than water use in France, which is only 165 liters/person/day.[20] Another source establishes the average per capita water use in 1994 between 364 and 230 liters per day for the Federal District and the State of Mexico respectively (probably before losses). Authorities attribute the increase in per capita use in the Federal District to the fact that it is more developed and has more commercial and industrial activity than the State of Mexico.[1] However, lower rates and metering in the Federal District can also influence the greater use of water.

Limited cost recovery

There is an enormous gap between the cost of water supply, a quarter of what is imported through inter-basin transfers from the Lerma and Balsas basins, and what is recovered from users. Among the reasons for the low cost recovery are illegal water connections, low rates and the low level of bill collection, specifically in the Federal District.

Cost recovery in the State of Mexico is much higher than in the Federal District. For example, the city of Toluca in the State of Mexico charges residential users 9.5 pesos (US$0.72)/m for a consumption of 30 m³, including a sanitation surcharge, the sixth highest rate among the country's top 25 municipalities.[21] This is still insufficient relative to the cost of bulk water from the Cutzamala system, at almost 10 pesos (US$0.78)/m, however. take into account the cost of water distribution and sanitation.

In 2004, the Federal District charged residential users 3.3 pesos (US$0.26)/m for the same consumption without any sanitation surcharge, the fourth lowest rate among the same municipalities.[21]​ The rest is effectively subsidized through the municipal and federal governments. In August 2007, a conflict arose between CONAGUA and the Federal District when CONAGUA increased the rate for water supplied through the Cutzamala system and the local government rejected it.

A raíz de estos retos, se han creado dos programas principales. La Comisión Nacional del Agua inició un programa de sostenibilidad del agua de 2800 millones US$ en 2007 para el abastecimiento de agua en grandes cantidades, drenaje y tratamiento de aguas residuales durante el período de 2007 a 2012. De forma paralela, el gobierno del Distrito Federal inició un plan medioambiental de 15 años que también incluía el drenaje y el tratamiento de aguas residuales. De forma adicional, hace hincapié en la conservación y la reutilización del agua mediante la recarga de los acuíferos. Ambos planes tienen como objetivo reducir el agua no rentable.

Water Sustainability Program

In November 2007, President Felipe Calderón initiated a US$2.8 billion water sustainability program for the Valley of Mexico (Program for the Water Sustainability of the Valley of Mexico Basin) until 2012. The program expands the previous program for the sanitation of the Valley of Mexico. Its objectives are to prevent major floods, such as the Tabasco flood of 2007, treat all collected wastewater and reduce overexploitation of groundwater.[22]​.

Water supply and exchange. An additional 14 m/s of water will be transported from various sources. The largest of these imports (5 m/s) will be groundwater from the Tula Valley north of the Valley of Mexico Metropolitan Area, where the amount of wastewater has increased after many years of irrigation with untreated wastewater, at a cost of US$255 million. The second largest source of additional water will be mobilized through an exchange of treated wastewater for clean water currently used for irrigation in the Vaso de Cristo area (4m3/s), at a cost of 140 million. As part of the "rehabilitation" of existing sources, it is expected to expand the Cutzamala system by 3 m/s, at a cost of US$275 million. Finally, 2 m/s of the Guadalupe dam in the State of Mexico will be available at a cost of US$40 million.

Stormwater drainage and wastewater treatment. The program provides for the construction of the East Emitter in parallel to the Central Emitter. In February 2009, CONAGUA supervised the acquisition of the first of three tunnel boring machines from the German company Herrenknecht. The new TBM has been used to begin excavations of the tunnel in April 2009. All work on the tunnel system is expected to be completed in September 2012, at an expected cost of 13 billion MXP (approx. 1 billion US$).[23]​.

Apart from the discharge from the Emisor Oriental, 23 m/s would be treated in a wastewater treatment plant planned in El Salto (Hidalgo) "El Salto (Hidalgo)"), to supply water to the Tula irrigation district.[12] Almost half of the investment (US$1.28 billion) will be allocated to the construction of 6 wastewater treatment plants, of which the El Salto plant will be the largest with difference.[12]​.

Achieving the program's goal of supplying water to a growing population and reducing aquifer pressure is based on the assumption that leakage is reduced from 36% in 2005 to 25% in 2030.

Financing. The program is being funded from the following sources:.

• - Private sector: Wastewater treatment plants are expected to be financed by the private sectors as Build-Operate-Transfer (COT) projects.

• - Federal Government: the Federal Government directly finances some of the works, carried out by CONAGUA.

• - Trust No. 1928, created by the Federal District, the State of Mexico and the Federal Government, will finance part of the works. The trust is replenished through payments made by the Federal District and the State of Mexico for the supply they receive of water in large quantities from CONAGUA. This is financially managed by the National Bank of Public Works and Services Banobras, with CONAGUA acting as technical coordinator. The trust was amended in November 2008 in order to allow funding for a wider range of projects.[24]​.

• - A metropolitan fund, established at the national level for infrastructure investments, also finances some works.

Some of the investments could be delayed due to the deteriorating fiscal situation at the federal level.[12]​.

Environmental plan

With the objective of complementing the SARP, the Federal District began in 2007 an environmental plan (Green Plan) aimed at the sustainable development of the district that focuses on seven main axes, one of which is water. In 2008 it had a budget of US$6 million.[25] Regarding water, it is expected to achieve a balance in the aquifer with the reduction of residential use of water, the decrease in network losses, the increase in reuse and treatment of wastewater and the creation of parks around lakes Tláhuac and Xochimilco. More specifically, it is hoped to increase aquifer recharge through land use changes and recharge wells; metering all users by 2010 and charging all users for water; the identification and regularization of illegal connections; the construction of tertiary wastewater treatment plants to inject them into the aquifer. The plan is expected to relieve aquifer pressure by 6.8 m/s, including 3.3 m/s with leakage reduction, 1 m/s through water conservation, and 2.5 m/s with groundwater recharge with treated wastewater.[26][27] These measures together, if successful, will reduce groundwater extraction in the Valley of Mexico Metropolitan Area by 10% and overconsumption by 25%, but they are still insufficient to create a balance between extraction and recharge.

Entre las últimas respuestas a los retos del agua de la Zona Metropolitana del Valle de México se encuentra, una ambiciosa campaña de conservación del agua iniciada en 1989, así como un aumento de la medición y una reducción de las fugas con la participación del sector privado iniciados a principios de los años 90.

Water conservation program in the 90s

In 1989, at the same time as introducing stricter national water efficiency standards for household appliances, Mexico City began an ambitious program to replace conventional toilets (with 16 liters) with 6-liter models; Through this program, 350,000 toilets were replaced in 1991. The program also included a large-scale public information campaign and an increase in water rates.[28] The impact of the programs is difficult to evaluate, since the available figures on water consumption are difficult to compare over the years because it is not clear whether they include water losses and whether they refer only to residential consumption or total consumption.

Private sector participation from 1993 to 2007

Manuel Camacho Solís, the head of the Federal District Government from 1988 to 1997 and appointed by President Carlos Salinas (PRI), led the process of private sector participation in water supply in Mexico City in the early 1990s. At that time, water revenues were extremely low, no customer database was in operation, virtually no measurements were available, and there was low bill collection efficiency. At least 22% of clients did not receive bills, in part because water connections were made by one department and billing was managed by another that did not receive any information about water connections from the previous department.[29]​.

In November 1992, tenders were launched; In March 1993, the results were published and in November 10-year service contracts were signed with four companies, each for a block of the capital:.

• - Block 1 with four northern districts was granted to SAPSA (Servicios de Agua Potable S.A.), formed by the large Mexican construction company Ingenieros Civiles Asociados (ICA), together with the Banamex bank and the French company Générales Des Eaux (Vivendi).

• - Block 2 with three districts was granted to IASA, (Industrias del Agua S.A.), which was formed by businessmen from Monterrey and the British company Severn Trent.

• - Block 3 with the impoverished area in the southeast was attributed to TECSA (Tecnología y Servicios de Agua S.A.), which was composed of Bancomer, Bufete Industrial and the French company Lyonnaise Des Eaux-Dumex (SUEZ-Ondeo Services), as well as the British company Anglian Water.

• - Block 4 with five prosperous delegations was awarded to AMSA (Agua de México S.A.), which was formed by the GUTSA group and the British company North West Water International.

The private sector participation process is divided into three phases:

• - First phase (1994-1995): updating the user registry.

• - Second phase (1995-1998): reading of measurements, billing and some aspects of collection.

• - Third phase (1998-2003): detection and repair of leaks, extension and rehabilitation of the secondary rehabilitation network.

The city remained in charge of the main water production, treatment and distribution infrastructure, as well as some aspects of collection and sanitation infrastructure. He also established water rates. The first two phases were successful. Under the contracts, the number of metered connections grew from virtually none in 1994 to 1,264,500 in 2002, reaching more than 90% of all users.[30]​ However, the third phase was not as successful.[30][31][32]​.

Between 1994 and 1998, the amount invoiced increased by almost 30% in real terms. But the amount collected stagnated, since the private operators were not in charge of collecting tickets. The collection efficiency actually decreased from 84% to 69%[33]​ The service remained unchanged in terms of intermittency of supply and water quality, since these aspects were not part of the contracts. Rates and cost recovery also did not change, as revenues covered less than 75% of operating costs.[29]​ The third billing phase that increased responsibility for the private sector was abandoned after the PRD won the elections in 1997 and contracts were renegotiated.[29]​.

Initially, PRD president Andrés Manuel López Obrador (2000-2005) renewed the contracts in 2004 for another five years,[34] but his successors terminated them shortly before their expiration. All aspects of service delivery reverted to SACM, which had limited capacity to implement the ambitious objectives set out in the environmental plan for reducing non-profitable water and improving bill collection.

Valley of Mexico Sanitation Project

In 1996, the Inter-American Development Bank (IDB) approved a US$365 million loan for the Valley of Mexico Sanitation Project, in parallel with a US$410 million loan through Japan's Overseas Economic Cooperation Fund. The IDB project, which was closed in 2005, provided for the construction of 4 wastewater treatment plants with a total capacity of 74.5 m/s, as well as the rehabilitation of drainage systems.[35]​.

A pesar de que en la actualidad el 90% de la población mundial cuenta con fuentes de agua potable mejoradas, se estima que para 2050 el 25% de la población mundial viva en un país con carencias hídricas debido a la mala distribución y el mal manejo del agua; afectando principalmente los países con pobreza, teniendo repercusiones en la alimentación y la salud de sus habitantes. Se cree que la cantidad de agua dulce en el planeta es suficiente para cubrir las necesidades de la población, pero o se cuenta con la cultura del cuidado y saneamiento de las fuentes de gua potable.

Lo Objetivos de Desarrollo Sostenible se establecieron el 25 de septiembre de 2015 y se estima que para 2030 todos los puntos establecidos sean cubiertos y solucionados para lograr una mayor convivencia entre los habitantes de cada país y mejorar la calidad de vida del hombre a nivel mundial. Lo que se busca hacer a través de este objetivo dentro de los Objetivos de Desarrollo Sostenible es "garantizar la disponibilidad y la gestión sostenible del agua y el saneamiento para todas y todos".[36]​.

Goals of objective 6[37]​

6.1 Achieve universal and equitable access to drinking water at an affordable price for all.

6.2 Achieve access to adequate and equitable sanitation and hygiene services for all and end open defecation, paying special attention to the needs of women and girls and people in vulnerable situations.

6.3 Improve water quality by reducing pollution, eliminating dumping and minimizing the release of hazardous chemicals and materials, halving the percentage of untreated wastewater and significantly increasing recycling and safe reuse globally.

6.4 Significantly increase the efficient use of water resources in all sectors and ensure the sustainability of freshwater extraction and supply to address water scarcity and significantly reduce the number of people suffering from water lack.

6.5 Implement integrated water resources management at all levels, including through cross-border cooperation, as appropriate.

6.6 Protect and restore water-related ecosystems, including forests, mountains, wetlands, rivers, aquifers and lakes.

6.a Expand international cooperation and support to developing countries for capacity building in water and sanitation activities and programs, such as water harvesting, desalination, efficient use of water resources, wastewater treatment, recycling and technologies for this.

6.b Support and strengthen the participation of local communities in improving water and sanitation management.

• - Drinking water and sanitation in Mexico.

• - Management of water resources in Mexico.

• - Politics of Mexico.

• - National Water Commission Archived July 9, 2017 at the Wayback Machine.

• - Government of the Federal District of Mexico.

• - Mexico City Water System (SACM).

• - Water Commission of the State of Mexico.

• - UNESCO: World Water Resources Assessment Programme: case study: Sustainable urban water management in the State of Mexico, 2006 in English.

The climate of the Valley of Mexico ranges from a semi-arid zone in the north to a tropical zone in the south. The valley has annual rainfall of 700 millimeters (27.6 in), which is concentrated in the months of June to September/October and during the rest of the year there is little or no rainfall. Today, there are hardly any permanent rivers; Therefore, groundwater is the main water resource of the valley.

The valley does not have any natural drainage outlet for water coming from the slopes, which makes the city vulnerable to flooding. This was opened artificially through the use of canals and tunnels (work began in the 19th century) and what used to be Lake Texcoco was completely drained.

The rural southern part of the Federal District and the Valley of Mexico, especially the Chichinautzin mountain range, is the most important natural recharge zone for the Mexico City aquifer due to the relatively high levels of precipitation and the high permeability of its basalt.[1]​.

Management of water resources. The National Water Commission (CONAGUA) is responsible for the management of water resources in Mexico, including the granting of water extraction and wastewater discharge permits.

Water supply and sanitation. The National Water Commission also supplies water in large quantities to the Federal District and parts of the State of Mexico through the Cutzamala and Lerma systems.

In the State of Mexico, the State Water Commission purchases bulk water from CONAGUA, transmits it through its own bulk water infrastructure, and sells it to 57 municipalities, with 4.1 million inhabitants. The State Water Commission also monitors water quality, provides technical assistance to municipalities for water disinfection and sewer cleaning, operates wastewater pumping stations and five wastewater treatment plants, empties septic tanks, and supplies water by tanker trucks in emergency situations. It also provides training and assistance to municipalities in the establishment of municipal public services (operating organizations).[2] Each of the 59 municipalities of the State of Mexico and the municipality of the State of Hidalgo that are part of the Metropolitan Zone of the Valley of Mexico are responsible for water supply and sanitation.

Mexico City's municipal public water supply service, Sistema de Aguas de la Ciudad de México (SACM), is responsible for water supply and sanitation in the Federal District. Its director is appointed by the district government.

Contenido

La infraestructura hídrica de la Zona Metropolitana del Valle de México está formada por infraestructura para el abastecimiento de agua en grandes cantidades y la distribución de agua (abastecimiento de agua), la recolección de aguas residuales, la recolección de aguas pluviales y el tratamiento de aguas residuales (saneamiento), y el riego principalmente con aguas residuales.

Water supply

The Federal District and the State of Mexico together had 1,089 registered wells with a depth of 70 to 200 meters in 1994. These do not include the wells commissioned by the National Water Commission, which are deeper. There are also a large number of unregistered wells, many of which are located in the State of Mexico. Generally, the wells are located in four different well fields. These are labeled as Southern (or Xochimilco), Metropolitan, Eastern (or Texcoco region), and Northern well fields.[1]​.

Apart from these well fields, Mexico City's bulk water supply infrastructure is made up of two systems: Lerma and Cutzamala. The Lerma system, built in the 1940s, transfers 4.8 m/s of water (6% of the total water supply for the Metropolitan Zone of the Valley of Mexico) from well fields in the upper basin of the Lerma River west of Mexico City. The Cutzamala system was built in stages from the late 1970s to the late 1990s to transfer 14.9 m/s (19% of the total supply) of water from the Cutzamala River in the Balsas basin, southwest of the Metropolitan Area of ​​Mexico City, for use as drinking water, for which it was raised more than 1,000 meters. It uses 7 ponds, a 127 km long aqueduct with 21 km of tunnels, 7.5 km of open canals and a water treatment plant. Its cost was US$1.3 billion.[3]​ Although it provides Mexico City with more than 20% of its water, the Cutzamala system currently operates at only 47% of its total capacity.[4]​ Both systems are launched by the National Water Commission.

The Federal District's water distribution system incorporated almost 11,000 kilometers of distribution lines and 243 storage tanks with a capacity of 1.5 million cubic meters in 1994. Water from different sources is added to common distribution systems. The Federal District has also put into operation a water transmission line (the Peripheral Aqueduct) that transports water from the Cutzamala system (entering the distribution system from the west) to the southwestern and eastern part of the district. The State of Mexico system has almost 800 kilometers of distribution lines and 32 storage tanks with a capacity of 440,000 cubic meters. The State of Mexico puts into operation the 49 kilometers of water distribution lines (the Macrocircuit) to transport water from the west side of the service area (including water imported from the Cutzamala-Lerma system) to the east side. This transmission line is being upgraded to increase the volume of water taken from the Cutzamala-Lerma system to 7.3 cm and provide service to the eastern area. The State Water Commission puts the Macrocircuit into service.[1]​.

Combined sewer system

The Valley of Mexico Metropolitan Area is served by a unified combined sewer system that collects municipal wastewater, industrial wastewater, and stormwater. This includes 11.8 km (7.4 miles) of pipelines,[5]​ 68 pumping stations, numerous dams, lagoons, and flow control reservoirs, 111 kilometers of open canals, 42 kilometers of rivers used primarily for drainage, and 118 kilometers of tunnels and underground collectors (interceptors and emitters).[1]​ The three interceptors are as follows:.

• - The western interceptor (Interceptor del Poniente) flows into the Nochistongo channel, which finally joins the central emitter;.

• - The Central Interceptor flows into the Central Emitter (Deep Drainage) and then into the Salto River of the State of Hidalgo, near the Requena Dam, from where it flows to the Mezquital Valley; and.

• - The eastern interceptor (Interceptor del Oriente) empties into the Grand Canal, then passes through the old and new tunnels of Tequixquiac and, finally, empties into the Salado River.[6]​.

The total low flow rate of the Valley of Mexico Metropolitan Area, which is primarily composed of untreated municipal wastewater, was estimated at 44 m/s in 1993. During the rainy season, the region experiences many high-intensity, short-duration storms. A single storm can produce up to 70 millimeters (about 3 inches) of precipitation, which represents about 10 percent of the total annual precipitation. Taking this rainfall pattern into account, the overall drainage system was designed to transport 200 m/s over a 45-hour period.

Until 1910, the Grand Canal operated purely by gravity with an inclination of 19 cm per km. Over the next five decades, its inclination was reduced to 10 cm per km due to land subsidence of 7 meters. Some large pumps were installed in an attempt to maintain its capacity.[6]​[7]​ After the major floods of 1950 and 1951, it became clear that the Grand Canal could no longer protect the city against flooding and the creation of a deep drainage system was proposed for the first time. In 1959 studies on the system began; Its construction began in 1967 and was completed in 1975. It consists of a deep tunnel, the Central Emitter, with a length of 68 km and a depth of up to 250 m. Today it constitutes by far the most important element of Mexico City's drainage system. The system was designed for a flow of 170 m/s. However, due to additional land settlement, the inclination of the Grand Canal became zero in 1990 and negative in 2000. Despite the installation of additional pumps, the capacity of the Grand Canal decreased from 80 m/s in 1975 to 15 m/s in 2008. This in turn affected the Central Emitter, which had been designed to be closed during the dry season for maintenance. Due to the settlement of the Grand Canal, the continually filled with water, making it impossible to inspect it for problems or maintain it, so maintenance could not be carried out between 1995 and 2008. The tunnel has deteriorated due to excess loading and corrosion of its 65.62m (20 ft) diameter walls[5]​ and its capacity has been reduced to 120 m/s. In 2008, it underwent maintenance for the first time in more than 12 years.

Reuse for other purposes

Water reuse activities in the Valley of Mexico Metropolitan Area officially began in 1984 under the national program for efficient water use, including the recharge of aquifers with stormwater and reclaimed municipal wastewater, as well as the use of reclaimed wastewater in the industrial and service sectors. This national program included the creation of new wastewater discharge regulations by the Federal District and, in 1990, provisions were established for an industrial pretreatment program, an important prerequisite for any reclamation and reuse activity. However, little information is available on the extent and success of industrial pretreatment programs.

Within the service area of ​​the Federal District, the 2.62 m/s of reused treated wastewater is distributed as follows:

• - 83 percent for the irrigation of urban gardens and recreational reservoirs.

• - 10 percent for industrial uses.

• - 5 percent for agricultural irrigation, and.

• - 2 percent for commercial uses such as car washing.

Industries recycle and reuse wastewater generated by themselves or municipalities. For example, 26 private companies in the Vallejo area began a reuse program in 1989 with the establishment of a for-profit company: Aguas Industriales de Vallejo. The company rehabilitated a former municipal wastewater treatment plant and began distributing reclaimed water to its shareholder companies at three-quarters the cost of government-supplied drinking water.

A major wastewater reclamation and reuse project exists at Lake Texcoco along with other flood control and dust removal programs. Between floods, the lake's shallow saline bottom could dry out and produce strong dust storms. In response to this problem, the Texcoco plan was established in 1971. The solution was to create smaller permanent ponds within the extensive, intermittent lake bottom and rehabilitate problem areas for further urban and agricultural expansion through windbreaks, revegetation, agricultural irrigation and drainage improvements. Artificial and more permanent lakes were created by applying the knowledge obtained from the problem of subsidence. High pumping rates allowed the clays to consolidate and the former lake bottom to drop by about 4 meters in places. The reuse component of Texcoco's plans includes the construction of a wastewater treatment system through a facultative lagoon and the reclamation of rainwater collected for agricultural irrigation. Therefore, the drinking water currently used for this purpose will be replaced.

The Federal District built two pilot treatment plants in 1983 in order to study their potential for advanced treatment of secondary effluent wastewater for potable reuse and to analyze the potential to treat contaminated groundwater. Based on the results of the experimental treatment plants, new treatment facilities with a capacity of 0.3 m/s were built and designed for groundwater treatment and direct potable reuse. The stated goal of the reuse project was to mix reclaimed wastewater with treated groundwater and introduce the mixture directly into the distribution system. Currently, reclaimed wastewater is being used for non-potable purposes.[1]​.

Artificial groundwater recharge

Artificial groundwater recharge is currently being carried out in the Metropolitan Zone of the Valley of Mexico using flood water and treated wastewater.

Artificial flood water recharge has been carried out in the area since 1943 as a method of flood mitigation rather than as a method of groundwater recharge. Initial projects involved surface runoff retention and dispersion, channel modifications, and infiltration wells. Many of these projects were carried out in the highly permeable basalt of the highlands and very high infiltration rates were achieved during periods of heavy rainfall. Artificial flood water recharge using injection wells was first developed in the Federal District around 1953. However, half of the wells were subsequently closed due to operational problems. In 1970, a series of approximately 56 wells were developed for the purpose of stormwater disposal. These wells together could contain up to 35 m/s of water. Although the wells were not designed for recharge purposes, stormwater likely reached the aquifer.

The Texcoco project mentioned above has carried out studies on the indirect potable reuse of reclaimed wastewater through artificial recharge of the aquifer using secondary and advanced municipal wastewater treatment. The final effluent can be used in infiltration ponds or injection wells. In an independent program carried out by the Federal District, a pilot plant injected water treated with advanced processes directly into the aquifer at a rate of up to 0.05 m/s. Monitoring wells were used to evaluate changes in water quality and pressure levels.[1]​.

Entre estos, se incluyen la sobreexplotación de agua subterránea, el hundimiento de tierra, el riesgo de grandes inundaciones, el impacto de la creciente urbanización, la baja calidad del agua y el suministro intermitente, el uso ineficiente del agua, un índice bajo de tratamiento de aguas residuales, problemas de sanidad sobre la reutilización de aguas residuales para riego y la recuperación limitada de costos para el agua. La cobertura de la infraestructura en términos de acceso a una conexión de conductos de agua o al saneamiento, la cual se utiliza para supervisar los Objetivos de Desarrollo del Milenio para el abastecimiento de agua y el saneamiento, es casi universal en la Zona Metropolitana del Valle de México y como tal no constituye un reto.

Overexploitation of groundwater

The exponential growth of the population of the Mexico City Metropolitan Area has depleted its groundwater resources. The recharge of the aquifer is about 31.6 m/s which, when compared to the extraction of 59.5 m/s, results in an excess consumption of 28 m/s.[10]​ In 1983, systematic monitoring of the aquifer's water levels began. Since that time, the average annual decline in groundwater levels varies from 0.1 to 1.5 meters per year in different areas. Taking into account the current rate of depletion, the estimated storage volume has been calculated to be between 200 and 350 times the annual extraction. However, with a simplistic approach to the water balance, other realities are being ignored. For example, the aquifer is vulnerable to geologically induced water quality problems with increasing aquifer consolidation and depth and fragmentation of clay layers. Furthermore, it is possible that the actual available volume of the main aquifer was less than estimated due to the probable reduction in porosity with increasing depth. There are also practical and economic limitations to the pumping depth.[11]​.

What follows is the water balance of the Metropolitan Zone of the Valley of Mexico:

land subsidence

The city rests on the highly saturated clay of ancient Lake Texcoco. This soft foundation is collapsing due to over-extraction of groundwater. Land subsidence in Mexico City caused by overexploitation of groundwater over the last hundred years has been up to 9 meters and, as a consequence, damage has occurred to buildings, streets, sidewalks, sewers, stormwater drains and other infrastructure.

Flood

Flooding is common in Mexico City and swamps roads and sidewalks. In low-lying neighborhoods like Iztapalapa, residents are so accustomed to seeing a fetid sea of ​​sewage rising in the streets that they have built small dams in front of their houses.[5] Floods are caused by the joint subsidence and increased impermeability of the soil due to urbanization. According to the modeling, if the Central Emitter failed during the rainy season, a major flood would occur that would flood the historic center, the Mexico City International Airport, and the eastern districts of Mexico City.[12]​.

Increase in urbanization

Urban growth reduces soil permeability in groundwater recharge zones and increases the risk of flooding. It is estimated that the metropolitan area grows annually from 200 to 300 hectares in the recharge areas. For every square meter that is built, an average of 170 liters of recharge is lost per year. In this way, for every hectare that is built, water is lost for 500 families and the groundwater pressure additionally increases.[13] Between 1989 and 1994, the Federal District declared six environmental protection zones, mainly in forests and hillsides, with a total area of ​​almost 5,000 hectares in order to protect them from urbanization.[14]​.

Water quality and intermittent supply

Poor water quality is a concern at the source and point of use. Initially, it was believed that Mexico City's groundwater was protected from contamination by a thick impermeable layer. However, this layer has been fragmented due to land subsidence. Likewise, the natural upward flow of water in the Artesian Well has now been reversed due to groundwater depletion. In this way, it is believed that Mexico City's groundwater will become increasingly vulnerable to contaminants from landfills and industrial sites that leach into the aquifer. In addition, the deep drainage system penetrates the clay (aquitard) in some places of the main aquifer. During periods of heavy rain, wastewater leaks out of the deep tunnels into the surrounding subsoil and causes contamination of the aquifer.[15]​.

Distribution system leaks are a major concern for drinking water quality. When wastewater enters the ground from leaking sewers or other sources, when the pressure is low the leaking pipes become infiltrated with contaminated water. According to the Federal District Water Quality Laboratory, neighborhoods that experience more frequent service interruptions have worse quality water than neighborhoods with constant supply. The percentage of household tap water samples in compliance with the residual chlorine standard (0.2 milligrams/liter) was 87 to 100 percent of the tests carried out in 1993 and was notably low in the southeastern delegations (Iztapalapa, Tláhuac and Xochimilco). Household water storage tanks or tinacos are common on almost all house roofs and usually store water when the system's water pressure is inadequate. In many cases, the tanks are open and not cleaned regularly, which causes residual chlorine to dissipate and encourage the growth of microorganisms. The standard levels of chlorine (0.2 milligrams/liter) maintained in the distribution system upon reaching the customer's tap are not sufficient to eliminate microorganisms that may have penetrated the pipes.[15]​.

The water supply in many parts of the Metropolitan Area of ​​the Valley of Mexico is intermittent and the pressure is usually insufficient. Thus, users have to supplement their water supply with water purchased from tanker trucks or pipes. Occasionally, the water supply is even interrupted for several days, as happened in January 2009 when the Cutzamala system's water supply had to be reduced, cutting off water to 5.5 million people for three days.[16] This incident was followed by a second supply interruption in March 2009 and, more recently, a third interruption in April 2009. This third interruption was made in response to the alarmingly low levels of the city's water reserves. and carrying out repairs in the Cutzamala system. This lasted 36 hours and left more than five million city residents without water services. In response, the Mexico City government has had to implement an emergency supply response program, whereby water is provided in tanker trucks and bottles to residents of affected communities.[4]​.

Limited wastewater treatment and concerns about reuse for irrigation

As mentioned previously, only 15% of the wastewater in the Metropolitan Area of ​​the Valley of Mexico currently receives treatment. Stormwater, raw municipal wastewater and partially treated industrial wastewater are mixed together and reused for large-scale irrigation.

There are concerns about the health and environmental impact of reusing raw wastewater from Mexico City for irrigation. Crops grown with wastewater are limited to crops that are not eaten raw, but these limitations are difficult to enforce and farmers also grow vegetables using wastewater. According to a study by the International Water Management Institute (IWMI), these risks must be carefully considered, but the importance of this practice for the livelihoods of countless smallholders must also be taken into account.[17]​ Studies on soils irrigated with untreated wastewater for 50 years reveal an accumulation of heavy metals in the soil, but also that they accumulate to a lesser extent in plants.[18]​ According to another study, bacterial contamination has been found in the water of the canals used for bathing and in the groundwater used to supply drinking water from irrigated areas where wastewater has been reused, which has led to a high incidence of diarrhea and skin irritations.[19]​.

Inefficiency in urban water use

The Federal District has a non-profitable water level of 40%, close to the national average, which implies that only 60% of the water pumped into the system is actually billed. A large percentage of unprofitable water is not due to leaks, but to illegal connections. Additionally, SACM, the district's water department, has by far the lowest collection efficiency among the top 25 municipalities, only receiving payment for 40% of all its bills. Therefore, only 24% (60% billed, 40% bills paid) of the water pumped into the system is paid for. The level of non-profitable water in the State of Mexico is lower, so that the average level of the metropolitan area is 36%.

Figures regarding per capita water use are difficult to compare over time, as sources typically do not indicate whether water losses are included in the figures or not. The National Institute of Statistics and Geography established the Federal District's water use at 223 liters/day in 1999 (probably after losses), including 164 liters for residential use and 59 liters for industrial and commercial uses. This is only one-third of the average US water use, which is 603 liters/person/day. However, it is still a third higher than water use in France, which is only 165 liters/person/day.[20] Another source establishes the average per capita water use in 1994 between 364 and 230 liters per day for the Federal District and the State of Mexico respectively (probably before losses). Authorities attribute the increase in per capita use in the Federal District to the fact that it is more developed and has more commercial and industrial activity than the State of Mexico.[1] However, lower rates and metering in the Federal District can also influence the greater use of water.

Limited cost recovery

There is an enormous gap between the cost of water supply, a quarter of what is imported through inter-basin transfers from the Lerma and Balsas basins, and what is recovered from users. Among the reasons for the low cost recovery are illegal water connections, low rates and the low level of bill collection, specifically in the Federal District.

Cost recovery in the State of Mexico is much higher than in the Federal District. For example, the city of Toluca in the State of Mexico charges residential users 9.5 pesos (US$0.72)/m for a consumption of 30 m³, including a sanitation surcharge, the sixth highest rate among the country's top 25 municipalities.[21] This is still insufficient relative to the cost of bulk water from the Cutzamala system, at almost 10 pesos (US$0.78)/m, however. take into account the cost of water distribution and sanitation.

In 2004, the Federal District charged residential users 3.3 pesos (US$0.26)/m for the same consumption without any sanitation surcharge, the fourth lowest rate among the same municipalities.[21]​ The rest is effectively subsidized through the municipal and federal governments. In August 2007, a conflict arose between CONAGUA and the Federal District when CONAGUA increased the rate for water supplied through the Cutzamala system and the local government rejected it.

A raíz de estos retos, se han creado dos programas principales. La Comisión Nacional del Agua inició un programa de sostenibilidad del agua de 2800 millones US$ en 2007 para el abastecimiento de agua en grandes cantidades, drenaje y tratamiento de aguas residuales durante el período de 2007 a 2012. De forma paralela, el gobierno del Distrito Federal inició un plan medioambiental de 15 años que también incluía el drenaje y el tratamiento de aguas residuales. De forma adicional, hace hincapié en la conservación y la reutilización del agua mediante la recarga de los acuíferos. Ambos planes tienen como objetivo reducir el agua no rentable.

Water Sustainability Program

In November 2007, President Felipe Calderón initiated a US$2.8 billion water sustainability program for the Valley of Mexico (Program for the Water Sustainability of the Valley of Mexico Basin) until 2012. The program expands the previous program for the sanitation of the Valley of Mexico. Its objectives are to prevent major floods, such as the Tabasco flood of 2007, treat all collected wastewater and reduce overexploitation of groundwater.[22]​.

Water supply and exchange. An additional 14 m/s of water will be transported from various sources. The largest of these imports (5 m/s) will be groundwater from the Tula Valley north of the Valley of Mexico Metropolitan Area, where the amount of wastewater has increased after many years of irrigation with untreated wastewater, at a cost of US$255 million. The second largest source of additional water will be mobilized through an exchange of treated wastewater for clean water currently used for irrigation in the Vaso de Cristo area (4m3/s), at a cost of 140 million. As part of the "rehabilitation" of existing sources, it is expected to expand the Cutzamala system by 3 m/s, at a cost of US$275 million. Finally, 2 m/s of the Guadalupe dam in the State of Mexico will be available at a cost of US$40 million.

Stormwater drainage and wastewater treatment. The program provides for the construction of the East Emitter in parallel to the Central Emitter. In February 2009, CONAGUA supervised the acquisition of the first of three tunnel boring machines from the German company Herrenknecht. The new TBM has been used to begin excavations of the tunnel in April 2009. All work on the tunnel system is expected to be completed in September 2012, at an expected cost of 13 billion MXP (approx. 1 billion US$).[23]​.

Apart from the discharge from the Emisor Oriental, 23 m/s would be treated in a wastewater treatment plant planned in El Salto (Hidalgo) "El Salto (Hidalgo)"), to supply water to the Tula irrigation district.[12] Almost half of the investment (US$1.28 billion) will be allocated to the construction of 6 wastewater treatment plants, of which the El Salto plant will be the largest with difference.[12]​.

Achieving the program's goal of supplying water to a growing population and reducing aquifer pressure is based on the assumption that leakage is reduced from 36% in 2005 to 25% in 2030.

Financing. The program is being funded from the following sources:.

• - Private sector: Wastewater treatment plants are expected to be financed by the private sectors as Build-Operate-Transfer (COT) projects.

• - Federal Government: the Federal Government directly finances some of the works, carried out by CONAGUA.

• - Trust No. 1928, created by the Federal District, the State of Mexico and the Federal Government, will finance part of the works. The trust is replenished through payments made by the Federal District and the State of Mexico for the supply they receive of water in large quantities from CONAGUA. This is financially managed by the National Bank of Public Works and Services Banobras, with CONAGUA acting as technical coordinator. The trust was amended in November 2008 in order to allow funding for a wider range of projects.[24]​.

• - A metropolitan fund, established at the national level for infrastructure investments, also finances some works.

Some of the investments could be delayed due to the deteriorating fiscal situation at the federal level.[12]​.

Environmental plan

With the objective of complementing the SARP, the Federal District began in 2007 an environmental plan (Green Plan) aimed at the sustainable development of the district that focuses on seven main axes, one of which is water. In 2008 it had a budget of US$6 million.[25] Regarding water, it is expected to achieve a balance in the aquifer with the reduction of residential use of water, the decrease in network losses, the increase in reuse and treatment of wastewater and the creation of parks around lakes Tláhuac and Xochimilco. More specifically, it is hoped to increase aquifer recharge through land use changes and recharge wells; metering all users by 2010 and charging all users for water; the identification and regularization of illegal connections; the construction of tertiary wastewater treatment plants to inject them into the aquifer. The plan is expected to relieve aquifer pressure by 6.8 m/s, including 3.3 m/s with leakage reduction, 1 m/s through water conservation, and 2.5 m/s with groundwater recharge with treated wastewater.[26][27] These measures together, if successful, will reduce groundwater extraction in the Valley of Mexico Metropolitan Area by 10% and overconsumption by 25%, but they are still insufficient to create a balance between extraction and recharge.

Entre las últimas respuestas a los retos del agua de la Zona Metropolitana del Valle de México se encuentra, una ambiciosa campaña de conservación del agua iniciada en 1989, así como un aumento de la medición y una reducción de las fugas con la participación del sector privado iniciados a principios de los años 90.

Water conservation program in the 90s

In 1989, at the same time as introducing stricter national water efficiency standards for household appliances, Mexico City began an ambitious program to replace conventional toilets (with 16 liters) with 6-liter models; Through this program, 350,000 toilets were replaced in 1991. The program also included a large-scale public information campaign and an increase in water rates.[28] The impact of the programs is difficult to evaluate, since the available figures on water consumption are difficult to compare over the years because it is not clear whether they include water losses and whether they refer only to residential consumption or total consumption.

Private sector participation from 1993 to 2007

Manuel Camacho Solís, the head of the Federal District Government from 1988 to 1997 and appointed by President Carlos Salinas (PRI), led the process of private sector participation in water supply in Mexico City in the early 1990s. At that time, water revenues were extremely low, no customer database was in operation, virtually no measurements were available, and there was low bill collection efficiency. At least 22% of clients did not receive bills, in part because water connections were made by one department and billing was managed by another that did not receive any information about water connections from the previous department.[29]​.

In November 1992, tenders were launched; In March 1993, the results were published and in November 10-year service contracts were signed with four companies, each for a block of the capital:.

• - Block 1 with four northern districts was granted to SAPSA (Servicios de Agua Potable S.A.), formed by the large Mexican construction company Ingenieros Civiles Asociados (ICA), together with the Banamex bank and the French company Générales Des Eaux (Vivendi).

• - Block 2 with three districts was granted to IASA, (Industrias del Agua S.A.), which was formed by businessmen from Monterrey and the British company Severn Trent.

• - Block 3 with the impoverished area in the southeast was attributed to TECSA (Tecnología y Servicios de Agua S.A.), which was composed of Bancomer, Bufete Industrial and the French company Lyonnaise Des Eaux-Dumex (SUEZ-Ondeo Services), as well as the British company Anglian Water.

• - Block 4 with five prosperous delegations was awarded to AMSA (Agua de México S.A.), which was formed by the GUTSA group and the British company North West Water International.

The private sector participation process is divided into three phases:

• - First phase (1994-1995): updating the user registry.

• - Second phase (1995-1998): reading of measurements, billing and some aspects of collection.

• - Third phase (1998-2003): detection and repair of leaks, extension and rehabilitation of the secondary rehabilitation network.

The city remained in charge of the main water production, treatment and distribution infrastructure, as well as some aspects of collection and sanitation infrastructure. He also established water rates. The first two phases were successful. Under the contracts, the number of metered connections grew from virtually none in 1994 to 1,264,500 in 2002, reaching more than 90% of all users.[30]​ However, the third phase was not as successful.[30][31][32]​.

Between 1994 and 1998, the amount invoiced increased by almost 30% in real terms. But the amount collected stagnated, since the private operators were not in charge of collecting tickets. The collection efficiency actually decreased from 84% to 69%[33]​ The service remained unchanged in terms of intermittency of supply and water quality, since these aspects were not part of the contracts. Rates and cost recovery also did not change, as revenues covered less than 75% of operating costs.[29]​ The third billing phase that increased responsibility for the private sector was abandoned after the PRD won the elections in 1997 and contracts were renegotiated.[29]​.

Initially, PRD president Andrés Manuel López Obrador (2000-2005) renewed the contracts in 2004 for another five years,[34] but his successors terminated them shortly before their expiration. All aspects of service delivery reverted to SACM, which had limited capacity to implement the ambitious objectives set out in the environmental plan for reducing non-profitable water and improving bill collection.

Valley of Mexico Sanitation Project

In 1996, the Inter-American Development Bank (IDB) approved a US$365 million loan for the Valley of Mexico Sanitation Project, in parallel with a US$410 million loan through Japan's Overseas Economic Cooperation Fund. The IDB project, which was closed in 2005, provided for the construction of 4 wastewater treatment plants with a total capacity of 74.5 m/s, as well as the rehabilitation of drainage systems.[35]​.

A pesar de que en la actualidad el 90% de la población mundial cuenta con fuentes de agua potable mejoradas, se estima que para 2050 el 25% de la población mundial viva en un país con carencias hídricas debido a la mala distribución y el mal manejo del agua; afectando principalmente los países con pobreza, teniendo repercusiones en la alimentación y la salud de sus habitantes. Se cree que la cantidad de agua dulce en el planeta es suficiente para cubrir las necesidades de la población, pero o se cuenta con la cultura del cuidado y saneamiento de las fuentes de gua potable.

Lo Objetivos de Desarrollo Sostenible se establecieron el 25 de septiembre de 2015 y se estima que para 2030 todos los puntos establecidos sean cubiertos y solucionados para lograr una mayor convivencia entre los habitantes de cada país y mejorar la calidad de vida del hombre a nivel mundial. Lo que se busca hacer a través de este objetivo dentro de los Objetivos de Desarrollo Sostenible es "garantizar la disponibilidad y la gestión sostenible del agua y el saneamiento para todas y todos".[36]​.

Goals of objective 6[37]​

6.1 Achieve universal and equitable access to drinking water at an affordable price for all.

6.2 Achieve access to adequate and equitable sanitation and hygiene services for all and end open defecation, paying special attention to the needs of women and girls and people in vulnerable situations.

6.3 Improve water quality by reducing pollution, eliminating dumping and minimizing the release of hazardous chemicals and materials, halving the percentage of untreated wastewater and significantly increasing recycling and safe reuse globally.

6.4 Significantly increase the efficient use of water resources in all sectors and ensure the sustainability of freshwater extraction and supply to address water scarcity and significantly reduce the number of people suffering from water lack.

6.5 Implement integrated water resources management at all levels, including through cross-border cooperation, as appropriate.

6.6 Protect and restore water-related ecosystems, including forests, mountains, wetlands, rivers, aquifers and lakes.

6.a Expand international cooperation and support to developing countries for capacity building in water and sanitation activities and programs, such as water harvesting, desalination, efficient use of water resources, wastewater treatment, recycling and technologies for this.

6.b Support and strengthen the participation of local communities in improving water and sanitation management.

• - Drinking water and sanitation in Mexico.

• - Management of water resources in Mexico.

• - Politics of Mexico.

• - National Water Commission Archived July 9, 2017 at the Wayback Machine.

• - Government of the Federal District of Mexico.

• - Mexico City Water System (SACM).

• - Water Commission of the State of Mexico.

• - UNESCO: World Water Resources Assessment Programme: case study: Sustainable urban water management in the State of Mexico, 2006 in English.