Potable water is a water source that can be consumed by humans and does not contain high levels of any compounds that cause illness or disease. Potable water that is consumed or used and is rejected or otherwise contaminated with biological, organic or inorganic compounds becomes wastewater (or sewage). Other terms used include gray water and black water. Gray water is untreated household wastewater that has not come into contact with toilet waste. Gray water includes water from bathtubs, showers, bathroom wash basins, clothes washers and laundry tubs. Black water includes wastewater that contains contaminants, including sewage from toilets and sanitary fixtures. The terms domestic sewage and sanitary sewage are normally used to identify sewage containing a majority of residential household and human body waste matter.
Stormwater includes rainfall or snow melt that contacts impervious surfaces such as streets, roofs and parking lots. Stormwater runoff does not naturally absorb into the ground, and areas that are more developed and include larger paved areas typically will result in greater stormwater collection needs. Stormwater can collect many pollutants from the surfaces it contacts, including debris, oils, sanitary waste from animals, fertilizers and pesticides. As a result, it may require treatment similar to wastewater before being discharged to the environment.
A combined sewer system collects sanitary sewage contribution and stormwater contribution in a single collection system. In this context, sanitary sewage and stormwater are mixed and transported for treatment together. Combined sewer systems are no longer designed when building new collection systems, but many older areas were constructed with these types of systems and are still using them today.
Collection and treatment of wastewater is required to avoid an adverse effect on the environment or humans and animals that require water to live. A wastewater treatment plant receives the wastewater (influent) and puts it through preliminary, secondary and tertiary processes to create treated wastewater or effluent, which is nonpotable but safe for discharge to the environment.
For more information on wastewater and its treatment, refer to Wastewater Treatment Plant Pumps: Guidelines for Selection, Application and Operation.
