Discharge or waste dumping is the release of liquid waste out of the vessel, container or pipe enabled to contain or transport it; such as the dumping of wastewater into a channel or body of water, which pollutes more or less seriously depending on its degree of toxicity (dumping of toxic waste). The term is also used for discharges that are carried out on the ground. For gases, the term "emission" is preferably used (although one can also speak of "discharge of gases into the atmosphere"); while for solid waste it is common to use the term "landfill", particularly when the destination is a "landfill (garbage)". For the DRAE, "pouring" ("action of pouring") is also the "set of waste substances from any industrial process".

Discharges occur as a consequence of human activity, their impact on the environment is negative and must be minimized through appropriate corrective measures (waste management).

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Urban discharges, or sewage, are characterized by their organic pollution (fecal), dissolved or suspended, which is measured as a whole (without discriminating specific compounds) by their chemical oxygen demand (COD) and their biological oxygen demand (BOD).

The NTK (Total Kjeldahl Nitrogen) parameter denotes nitrogenous compounds, except nitrites and nitrates. This composition is decisive for its treatment "Treatment (engineering)"), which consists of the elimination of suspended solids and fats through primary treatment), followed by the elimination of dissolved organic matter through biological treatment in secondary treatment.

The typology of industrial discharges is very varied depending on the type of industry, and they must be treated before being discharged into the urban sewer (especially to eliminate possible toxins for the biological treatment of the urban treatment plant located at the end of the sewer), and even more so if they have to be discharged directly into the riverbed.