Sewage is the liquid waste discharged from a structure. It includes both black water and gray water and originates from sources such as toilets, bidets, baths, showers, washing machines, dishwashers, sinks, and in some situations rain gutters and road drains. The liquid waste travels from where it is created to the sewage treatment plant where it can be processed in a network of pipes or tunnels called a sewer. Sewage is mostly water, but can also contain many microbes and chemicals that can cause harm to many organisms. Most sewage in poor regions is not treated and may spread disease.
80% of sewage could be reused as graywater, instead, in cities, all sewage goes to large sewage treatment plants, and rural areas it goes to smaller sewage treatment plants. In very rural areas it goes into septic systems. This results in pollution in and around the water near cities, and a loss of nutrient rich irrigation water in rural areas.