Prevention

To keep our used water from spoiling our water resources, we have to remove the pollutants before the water gets back into the environment. In urban areas in most developed countries, the wastewater from homes, businesses and factories is collected by a system of underground pipes-- sewers-- which carry it to one or more central treatment facilites. Most of these are located near bodies of water into which the treated wastewater is discharged.

In the U.S., all such facilites must have a permit issued by the federal and/or state government, describing limits on the amounts of various pollutants which may be discharged. The U.S. EPA (Environmental Protection Agency) refers to these as NPDES (National Pollutant Discharge Elimination System) permits. Industries located in areas where they are not connected to a sewer can discharge directly into a waterway, but will need a permit, and will probably have to have their own treatment plants. Even industries which are connected to sewers may have to pretreat their wastewaters before discharging them into the sewers, because they may contain materials which will harm the sewers or the treatment plants-- or may be a danger to the people who work in maintaining the sewer system.

Homes in non-urban areas that are not connected to a sewer are usually required by their town to have on-site treatment systems. Most common for single homes are septic systems, which consist of a buried tank connected to a set of perforated pipes, embedded in gravel, which distribute the water into the soil. (The "Links" page has several references on this subject.) Larger housing complexes may have treatment systems based on the principles used in full-scale sewage treatment plants.