A new report called "Sick Water?", which says some two or more billion tons of wastewater was being discharged daily into rivers and seas across the world, has been launched at the World Water Day celebrations in Nairobi.
The report indicates that the wastewater was spreading disease to humans and damaging key ecosystems such as coral reefs and fisheries.
"Transforming wastewater from a major health and environmental hazard into a clean, safe and economically-attractive resource is emerging as a key challenge in the 21st century," said Ibrahim Thiaw, Division Director of the United Nations Environment Programme (UNEP) during the launch of the report.
He said managing wastewater was a challenge that will continue to intensify as the world undergoes rapid urbanization, industrialization and increasing demand for meat and other foods unless decisive action is taken.
Urban populations are projected to nearly double in 40 years from current 3.4 billion to over six billion people - but already most cities
lack adequate wastewater management due to aging, absent or inadequate sewage infrastructure.
Wastewater is a cocktail of fertilizer run-off and sewage disposal alongside animal, industrial, agricultural and other wastes.
The report says that the sheer scale of dirty water means more people now die from contaminated and polluted water than from all forms of violence including wars.
Dirty water is also a key factor in the rise of de-oxygenated dead zones that have been emerging in seas and oceans across the globe.
The report said many of the substances that make wastewater a pollutant-for example nitrogen and phosphorus-- can also be useful as
fertilizers for agriculture.
"Wastewater can also generate gases to fuel small power stations or be used for cooking, "it said.
The report notes that already some 10 per cent of the world's population is being supplied with food grown using wastewater for irrigation
and fertilizer and with better management and training of farmers this could be increased substantially.
The report, launched to coincide with World Water Day, goes to say that the concentration of nutrients in wastewater "could supply much of the
nitrogen and much of the phosphorous and potassium normally required for crop production. Other valuable micro-nutrients and organic matter contained in the effluent would also provide benefits".
It said reducing the volume and concentrations of wastewater will require multiple actions ranging from reducing run-off from livestock and croplands to better treatment of human wastes.
Others may involve investing and re-investing in nature's natural purification systems which include wetlands, mangroves and salt marshes.
Achim Steiner, UN Under-Secretary General and Executive Director of the UN Environment Programme (UNEP), said: "If the world is to thrive, let alone to survive on a planet of six billion people heading to over nine billion by
2050, we need to get collectively smarter and more intelligent about how we manage waste including wastewaters".
"The facts and figures are stark-pollution from wastewater is quite literally killing people, indeed two million children die annually as a result of contaminated water."
"The impacts on the wider environment and in particular the marine environment are also sobering," he added.
"But the report also points to the abundant Green Economy opportunities for turning a mounting challenge into an opportunity with multiple benefits.
"These include the savings from reduced fertilizer costs for farmers and incentives for conserving ecological infrastructure such as wetlands alongside new business and employment opportunities in engineering and natural resource management," Mr Steiner said.
Mrs Anna Tibajuka, Executive Director of UN-Habitat, said: "Urban and industrial wastewater composed of sediment, nutrients, organic matter, trace metals and pesticides, among others, adversely affects the entire food chain and thus human health".
"Many water and sanitation utilities, especially in developing countries, are forced to spend more financial resources in water treatment
due to increased pollution."
"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.
She expressed the hope that activities taking place globally today will raise public awareness of the water quality challenges facing humanity, and the need to commit to concrete remedial actions at all levels.
Christian Nellemann, a lead author of the report, said "Some estimates suggest that around 2 million tons of wastes are spilled into sewage systems every day and this may be producing well over two billion tons of polluted water every single day, 365 days a year, right into our freshwaters and oceans".