In today's modern society we have numerous uses for water both around the home as well as in commercial or industrial operations. This water becomes waste-water once it has been "used" - whether for washing dishes in a restaurant, flushing a toilet, or as part of a manufacturing process. Rainfall and runoff from streets and parking lots is also wastewater. These sources combine to produce almost one billion litres of waste-water on an average day. Waste water is also the water used for flushing, bathing, laundry, cleaning dishes, floor drainage etc. It is the water used by factories. Waste water flows into the sewer system and then to a regional waste water treatment plant. It is cleaned and returned to nature.