Multi-criteria analysis, Multi-objective analysis, also abbreviated as AMO, is an instrument that is used to evaluate various possible solutions to a given problem, considering a variable number of criteria, it is used to support decision making in the selection of the most convenient solution. For example, focusing on the issue of water resources linked to an urban conglomerate, multi-criteria analysis could be applied to one or several cases such as, for example, the following:

• - Combination of raw water sources for the supply of drinking water, such as: sea water, renewable groundwater, fossil water, surface water of a river or lake, rainwater, etc.;.

• - Type of treatment to be implemented for water purification, such as: desalination, complete traditional treatment, disinfection, etc.;

• - Position of the new drinking water treatment plants, such as: close to the source, close to an existing plant, in the center of gravity of the area to be supplied, etc.;

• - Type and location of wastewater treatment plants;

• - Use to be given to the waste water after its treatment, such as: irrigation, groundwater recharge, etc.

It must be considered that the procedure is a methodological aid to decision making, which must be considered with due caution, since in any case, in the multi-criteria evaluation process, as well as in other procedures used for the same purpose, subjective factors cannot be completely eliminated.

To minimize the risk, a specific committee is generally formed, made up of the main actors involved in the issue, such as: Local authorities of the town, regional and national authorities as the case may be, and representatives of civil society. The actors involved must reach consensus to establish, among other things:

• - The alternatives to be analyzed;

• - The objectives, variables, criteria and weights of relative importance for the defined criteria.

In a second phase, experts in the application of the method will apply the usual mathematical procedures (the “Scoring” method, the “Hierarchical Analytical Process” or another similar method), to conclude with a sensitivity analysis regarding the main variables, and in a third conclusive phase in which the results will be presented to the decision makers for validation, or to make the necessary adjustments.