The waste water , so called polluted water (see Pollution the water) are all water which is likely to contaminate the mediums in which they are poured.
This water is in general the by-product of a human use either domestic or industrial (from where the " term; water usées" of which it was made use).
The waste water is the water deteriorated by the human activities following a use domestic, industrial, artisanal, agricultural or different. They are regarded as polluted and must be treated.
They are sometimes described as gray water when it is about polluting matter water not very charged for example with water of domestic origin, resulting from the washing of the plates, the hands, the baths or the showers, and of black water when they contain various substances more polluting or more difficult to eliminate such as fecal Matières, produced Cosmétiques, or all types of industrial by-product mixed with water.
It can also be a question of water of flow of impermeable surfaces, thus water of Ruissellement of the parking bays are regarded as waste water because of presence of various pollutants like the Hydrocarbures or dust of pneumatic wear of the S.
In the majority of the countries and in particular in the urbanized mediums, the waste water is collected and conveyed by networks of sewer (also called network of Assainissement) either directly in the receiving medium, or in a station of treatment.
The purification of these substances is generally ensured by stations of purification of worn water. Whenever such installations do not exist, the natural environment is able, to a certain extent, to ensure its Autoépuration.
See also: Purification of water
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