The vast quantities of domestic, agricultural and industrial wastewater which are discharged into the environment everyday, are an untapped resource, according to the United Nations World Water Development Report. The report, released on March 22 on the occasion of World Water Day, argues that once treated, wastewater offers many benefits for human health and the environment, food and energy security as well as climate change mitigation. The heading of the press release even describes wastewater as the new black gold. However, a large proportion of wastewater is still released into the environment without being either collected or treated. It is estimated that globally, over 80% of all wastewater is discharged without treatment, especially in low-income countries.

“Wastewater is a valuable resource in a world where water is finite and demand is growing,” said Guy Ryder, Chair of UN-Water. “Everyone can do their bit to achieve the Sustainable Development Goal target to halve the proportion of untreated wastewater and increase safe water reuse by 2030. It's all about carefully managing and recycling the water that runs through our homes, factories, farms and cities,” he added. Over the past decades, agricultural water use has increased remarkably. The area equipped for irrigation has more than doubled, from circa 1.4 million km² in 1961 to almost 3.2 million km² in 2012. Total livestock has more than tripled from 7.3 billion units in 1970 to 24.2 billion in 2011. Aquaculture has grown more than twentyfold since the 1980s. Agriculture is by far the largest consumer of the Earth’s available freshwater, accounting for 70% of freshwater withdrawals.

In many countries of the world, wastewater is commonly used for agricultural irrigation. Estimates of the total area that is being irrigated with raw and diluted wastewater range from 5 to 20 million hectares, with the largest share in China. In Jordan, over 90% of treated wastewater is currently being used for irrigation. In Israel, treated wastewater already accounts for nearly half of all water used for irrigation. However, wastewater’s vast potential remains underexploited, especially in Africa.

But the report also warns against the dangers of water pollution, especially from agriculture. Water pollution from agriculture occurs when fertilizers and other agrochemicals are applied more heavily than crops can absorb them or when they are washed away. Nutrients can also be released by livestock production and aquaculture. The report says that agriculture can be a source of several other types of pollutants, including organic matter, pathogens, metals and emerging pollutants. In addition, over the last 20 years, new agricultural pollutants have emerged, such as antibiotics, vaccines, growth promoters and hormones that may be released from livestock and aquaculture farms. There are serious health concerns if water used for irrigation contains pathogens that can contaminate crops.

The report calls for improved wastewater management which includes reducing pollution at the source, removing contaminants from wastewater flows, reusing reclaimed water and recovering useful by-products. Treated wastewater can be a potential source of raw materials such as phosphorus and nitrates that can be turned into fertilizer. According to FAO estimates, 22% of global demand for phosphorus, a finite and depleting mineral resource, could be met by reusing treated wastewater. “In a world where demands for freshwater are continuously growing, and where limited water resources are increasingly stressed by over-abstraction, pollution and climate change, neglecting the opportunities arising from improved wastewater management is nothing less than unthinkable,” the report concludes. (ab)