Wastewater has been defined as the water discharged from a community after it has been fouled by various uses and containing waste, i.e. liquid or solid matter. It may be a combination of the liquid or water-carried domestic, municipal and industrial wastes, together with such groundwater, surface water and storm water as may be present.

Population growth, rapid urbanization, and increasing water supply and sanitation provision will all generate increased problems from wastewater pollution.

It has been estimated that the total global volume of wastewater produced in 1995 was in excess of 1,500 km3.

There is the understanding that each litre of wastewater pollutes at least 8 litres of freshwater, so that on this basis some 12,000 km3 of the globe’s water resources is not available for use each year. If this figure keeps pace with population growth, then with an anticipated population of 9 billion by 2050, the world’s water resources would be reduced by some 18,000 km3 annually.

At present, only about a tenth of the domestic wastewater in developing countries is collected and only about a tenth of existing wastewater treatment plants operates reliably and efficiently.

Some of the damage associated with inadequate handling of wastewater are:
increased direct and indirect costs caused by increased illness and mortality
higher costs for producing drinking and industrial water, resulting in higher tariffs
loss of income from fisheries and aquaculture
poor water quality, which deters tourists, immediately lowering income from tourism
loss of valuable biodiversity
loss in real estate values, when the quality of the surroundings deteriorates: especially important for slum dwellers where housing is the primary asset.

Untreated sewage affects over 70% of coral reefs, precious habitats are disappearing and biodiversity is decreasing, fishing and agricultural potential are being lost, while poor water quality is reducing income from tourism and the value of real estate.

The global burden of human disease caused by sewage pollution of coastal waters has been estimated at 4 million lost person-years annually.

In March 2003, the World Panel on Financing Water Infrastructure estimated that US $56 billion was needed annually for wastewater treatment in order to achieve the target on sanitation.

In the State of Mexico (Mexico), wastewater is generated approximately at the rate of 30 m3 per second (m3/s), about 19% of which is directly discharged without any kind of treatment.

Information from:
the 1st United Nations World Water Development Report: ‘Water for People, Water for Life’
the 2nd UN World Water Development Report: ‘Water, a shared responsibility’
the United Nations Environment Programme (UNEP) Magazine ‘Our Planet’ [PDF format – 1.11 MB]