Wastewater is used water that should be treated before being discharged from another source of water, so as not to cause further pollution to water resources. Black water comes from a variety of sources. Everything you flush in your toilet or flush down the floor is black water. Rainwater and streams, as well as various pollutants, run down the gutters and eventually end up in the sewage treatment plant. Wastewater can also return to agricultural and industrial sources.In terms of presence of water pollutants industrial wastewater can be difficult to manage than domestic wastewater (although it is increasingly difficult to treat household waste, due to the increasing number of medicines and personal care products found in domestic wastewater).

Many provincial and provincial governments have laws governing standards and requirements for purifying wastewater. Users of wastewater treatment plants must obtain permits or licenses from the local government, and these permits may also require additional treatment or restrictions on sewage disposal.. Provincial and district governments often assist local governments with funding to build and maintain infrastructure.