Non-point sources of sewage

Constructing municipal sewerage requires substantial capital investment, which is often not available. Even when capital is available, it may not make economic sense to invest in treatment facilities prior to completion of the reticulation network (e.g., in the Philippines). Rapid urbanization in many coastal areas, often in the form of unplanned squatter settlements, adds to the difficulty of providing sewerage and treatment infrastructure.

In such circumstances, providing water supply usually has a higher priority than sewage collection and treatment. Neighbourhoods are often provided with a municipal water supply before they receive sewerage to dispose of the increased volume of wastewater that results

As a result, non-point sources such as septic fields, and pit or overwater latrines, are a significant source of sewage contamination in many areas. In many countries significant reductions in sewage contamination could be achieved by converting pit or overwater latrines to septic tanks, by better design and construction of existing septic tanks, or by better provisions for septic sludge disposal.

The failure of on-site systems because of poor ongoing operation and maintenance (e.g., not emptying tanks or pits) is a common reason given for needing sewerage. Septic tanks can also be linked to stepped digestion tanks that produce effluent suitable for irrigating home gardens. There are also simple technologies, such as composting toilets and biogas generation, that are suitable for application in individual households or to small groups of them.