Turning two billion tons of wastewater into an economic resource could benefit human health, agriculture and the environment, says a new UNEP report released this month. Investing in clean water will pay multiple dividends from overcoming poverty to meeting Millennium Development Goals.

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. This is a challenge that will continue to intensify as the world undergoes rapid urbanisation and industrialisation and as demand for meat and other foods continue to rise.

Global populations are expected to exceed nine billion by 2050. Urban populations are projected to almost double in the next 40 years, from the current figure of 3.4 billion to over 6 billion people. Most cities already lack adequate wastewater management due to aging, absent or inadequate sewage infrastructure, however.

The report, entitled Sick Water?, describes how the way we produce our food uses 70-90% of the available fresh water. Much of this water is returned to the system with additional nutrients and contaminants. We have created a domino effect as downstream agricultural pollution is joined by human and industrial waste. This wastewater contaminates freshwater and coastal ecosystems, threatening food security, access to safe drinking and bathing water and providing a major health and environmental management challenge. Some two million tons of waste (up to 90% of wastewater, estimated to equal two or more billion tons), is being discharged daily into rivers and seas, spreading disease to humans and damaging key ecosystems such as coral reefs and fisheries. Marine dead zones already cover an area of 245,000 km2, approximately the same area as all the world's coral reefs.