The world's two billion tons of wastewater could supply much of the nitrogen, phosphorous and potassium required for crop fertilisation, says a report from the United Nations Environment Programme (UNEP).
The report, 'Sick Water', says a cocktail of agricultural, human and industrial waste is currently polluting freshwater supplies and marine ecosystems.
Between 80-90 per cent of all wastewater generated in less-industrialised countries is discharged untreated into water courses, leading to 1.8 million deaths amongst children under the age of five every year as a result of water-borne diseases.
The report cites contrasts Jakarta, where just 3 per cent of sewage reaches a treatment plant, to Sydney, where each citizen produces three times as much wastewater but almost 100 per cent of it reaches a treatment plant.
Jakarta has more than one million septic tanks but most are poorly maintained and often when they are emptied the contents are dumped untreated into waterways, says the UNEP.
However, the authors of the report argue that wastewater can be an asset instead of a pollutant, particularly in the agricultural sector, which uses up 70-90 per cent of all the human water consumption.
The report says 10 per cent of the world's population is already supplied with food grown using wastewater for irrigation and fertiliser, and with better management and training of farmers this could be increased substantially.
Notable successes include coastal areas of Fiji where pig waste was causing substantial marine pollution. It is now being captured in sawdust beds and shipped to nearby farms for use as fertiliser.
The UNEP report says investment in better wastewater management and sewage systems such as those seen in Fiji would benefit the health of people and marine ecosystems such as fishieries, on which many people rely for their livelihoods.
'Many water and sanitation utilities, especially in developing countries, are forced to spend more financial resources in water treatment due to increased pollution,' says Anna Tibajuka, executive director of UN-Habitat, which helped to compile the report.
'Excess nutrients and wastewater can also lead to uncontrolled growth of algae and aquatic plants such as water hyacinth, which cause practical problems for marine transportation, fishing and at intakes for water, hydro power and irrigation schemes,' she added.
Full UNEP report
|Graphic: Amount of water withdrawal and type of use by continent (source: UNEP)
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