Waste water is the water that emerges after fresh water is used by human beings for domestic, commercial and industrial use. This document will restrict itself only to the waste water generated due to domestic use.
By and large, it is fresh water that is used for a variety of domestic uses such as washing, bathing & flushing toilets. Washing involves the washing of utensils used in cooking, washing vegetables and other food items, bathing, washing hands, washing clothes.
The water that emerges after these uses contains, vegetable matter, oils used in cooking, oil in hair, detergents, dirt from floors that have been washed , soap used in bathing along with oils/greases washed from the human body. This water is referred to as “ Grey Water” or sullage.
Water used to flush toilets to evacuate human excreta is called “ Black Water” or Sewage.
Grey water is easier to purify as compared to black water, i.e sewage. However, the practice predominantly followed in India is to combine these two wastes to discharge into a public sewer or into a sewage treatment plant in a residential community/ building that has no access to a public sewer.