Septic tank
A septic tank is an underground chamber made of concrete, fiberglass or plastic through which domestic wastewater (sewage) flows for basic treatment. Settling and anaerobic processes reduce solids and organics, but the treatment efficiency is only moderate (referred to as "primary treatment"). Septic tank systems are a type of simple onsite sewage facility (OSSF). They can be used in areas that are not connected to a sewerage system, such as rural areas. The treated liquid effluent is commonly disposed in a septic drain field which provides further treatment. However, groundwater pollution may occur and can be a problem.
Water supply and sanitation in Kenya
The Citizen Report Card moreover indicates that septic tanks are often used for the disposal of wastewater from flush toilets in Mombasa. Pit latrine users from Nairobi, Kisumu and Mombasa indicated that some wastewater empties into storm sewers, soak-aways and cess pits designed for kitchen waste, thus causing environmental pollution. In 2001 a pollution incident occurred in the town of Embu. Raw sewage was discharged from sewage treatment works into a nearby river and caused the death of 28 people who used the water downstream for domestic purposes.