Wastewater crop irrigation risks health of nearly a billion people

Clean water supplies are dwindling around the globe. To grow their crops, farmers resort to using untreated wastewater, which could make them sick - to an even greater extent than previously thought, a study finds.

It's an area about the size of Germany: 29.3 million hectares (72.4 million acres) of cropland worldwide is mainly irrigated with what's flushed down the toilet, a study published in "Environmental Research Letters" reports.

Nature and Environment | 21.02.2018

That translates into a major health risk for all the people who eat the food that grows on that farmland.

As many as 885 million urban residents are being exposed to dangerous pathogens, including parasites and bacteria, according to the researchers' modeling.

Irrigation with untreated wastewater is especially an issue around bigger cities without proper sewage treatment, and - according to the study - particularly in China, India, Pakistan, Mexico and Iran.

Nature and Environment | 22.03.2017

"In most cases the farmers might not even know it," Pay Drechsel tells DW. He is project leader at the International Water Management Institute in Sri Lanka, and a co-author of the study.

Wastewater: a reliable source

Some farmers use wastewater on purpose to water their crops, Drechsel tells DW.

"It has a huge amount of nutrients," Drechsel points out. "We know of cases where farmers are fighting for the use of wastewater, even if there is fresh water available - then they don't have to pay for fertilizer."

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More modern wastewater treatment plants like this one in South Africa are needed around the world

Sometimes, wastewater might be the only water available at all, like around big cities in dryer regions - or also in Ghana, where Drechsel lived and worked for 11 years. There, all urban farmers use polluted water to irrigate their crops, he says. "There is no alternative."

In the majority of cases, however, the farmer thinks he is using fresh, clean water - when it isn't.

Globally, less than 10 percent of collected wastewater is treated. Together with rainwater, untreated wastewater ends up in rivers, gets diluted with what previously was clean drinking water, and enters the food chain.

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"The water still carries all the pathogens," Drechsel says. "It is far beyond anything that is allowed for drinking or irrigation."

Untreated wastewater might contain parasite eggs or bacteria leading to cholera - but above all bacteria causing diarrhea. According to Drechsel, children below the age of five are the most sensitive to diarrhea, often with fatal consequences.

Environmental impact

Apart from being a health risk, it's also an environmental issue. If sewage enters lake and rivers, it can contaminate waters and harm ecosystems.

In 2013, researchers from Ghana and Uganda examined domestic wastewater from Old Fadama, Ghana's biggest urban slum

"Wastewater from this community has potential deleterious environmental implications," the study found.

Iran KW 17 2014 verseuchtes Wasser

Wastewater entering a reservoir in Iran caused this massive fish die-off

The fouled water was extremely low in oxygen, and if this were to reach natural water bodies in the dry season, it would killing fish and other aquatic life - which is a common occurrence.

When sewage polluted River Trent in North Staffordshire in the United Kingdom in September 2016, more than 15,000 fish died.

Wastewater also contains high amounts of phosphates and other substances that fuel algae growth, sucking even more oxygen out of the water and creating a so-called "dead zone" where fish and other animals cannot live.

According to WWF, more than 400 areas around the world have been identified where this oxygen-depletion, also known as eutrophication, takes place. 

Wash your vegetables!

In Ghana, farmers around large cities mainly grow vegetables, Drechsel says.

"Vegetables are cash crops number one, especially exotic leafy vegetables." Such crops  require regular irrigation, unlike most staple foods such as grains.

Nearly a million people in urban Ghana eat vegetables produced with polluted water every day, he says.

Markt in Katar Doha

Consumers do not know that the vegetables they buy might be irrigated with wastewater

In 2004, a study estimated that between 6 and 20 million hectares of croplands are watered with untreated wastewater.

With this number now up to almost 30 million hectares, the recent study found the problem to be even bigger than previously thought.

Boiling or washing vegetables thoroughly before consumption will remove many pathogens.

"The risk awareness, is very, very low," Drechsel says. "We cannot just tell them to wash their vegetables, because they wouldn't know why."

He calls for campaigns to raise awareness about those health risks, so that there will be pressure from consumers.

Clean water is getting scarce

The World Health Organization estimates that more than 10 percent of the world's population consumes food produced with wastewater.

That amount might even increase in years to come.

Infografik Wasserbedarf weltweit 2000 bis 2050 Englisch

Global water demand is rising

"Wastewater is the only source of water that actually increases in quantity as population and water consumption grows," Drechsel points out.

The UN estimates that the amount of wastewater produced annually is about "six times more water than exists in all the rivers of the world."

"A livelihood opportunity for many millions"

Chris Scott, professor for Geography and Development at the University of Arizona points out that using wastewater for irrigation is not per se a bad thing.

"It represents a livelihood opportunity for many millions of smallholder farmers, contributes to global food security and recycles crop nutrients that would otherwise foul natural waterways," he tells DW.

Without, he adds, "developing countries in particular will be unable to meet the globally accepted Sustainable Development Goals."

The practice of wastewater irrigation, though, urgently needs to be managed. Scott suggests on-farm water treatment, protective clothing for farmers, improved hygiene in markets and effective vegetable-washing in kitchens.

Wastewater could also be converted industrially into fertilizer. A plant to do so is being built in Accra, Ghana, Drechsel says.

From his experiences in Ghana, Drechsel doubts that improved wastewater treatment "will happen so quickly."

The more important step it is to back away from eating raw, unwashed fruit and vegetables.

A finite resource

Water is fundamental to sanitation, healthy ecosystems and human survival. It's also a finite resource and lack of safe water could soon become a serious challenge to sustainable development. But if well and equitably managed, water can play a key role in strengthening the resilience of social, economic and environmental systems.

Down the drain

Food waste and water waste are closely linked. Agriculture accounts for around 70 percent of human water consumption. Each year, around 500 billion cubic meters of water are wasted growing crops that will never be eaten. Meat production requires more water than vegetables - but even your morning coffee needed 140 liters to make one cup.

Changing weather

Changing climatic conditions are leading to irregular rainfall patterns that complicate planning for water supply and increase water insecurity. This hits communities that depend on farming and agriculture particularly hard. In recent months, many have suffered from either short bouts of heavy rain - resulting in floods and loss of crops - or droughts that bring food shortages.

Less moo, more H2O

Livestock production is one of the most water-heavy industries. More than 15,000 liters are needed to produce one kilogram (2.2 pounds) of meat. Rising demand for beef and dairy products means less water is available for human consumption and sanitation, so a diet based on vegetables, pulses and grains is key to saving water.

The water polluters in your closet

The clothing industry is one world's worst water polluters, dumping thousands of gallons of chemical residue into rivers and oceans each year - mainly in developing countries. Laundry also uses up large amounts of water, and releases polluting detergents into ecosystems.

Ancient wisdom

As the global human population grows, so does its demand for water. But traditional techniques for harvesting rainwater have helped people in India, sub-Saharan Africa and South America to survive long dry periods and can be replicated in other parts of the world. With a little ingenuity, regular people everywhere can harvest and reuse rainwater at home, too.

From water world to plastic planet

Plastic waste is a major problem in waterways, and causes huge damage to marine life. But demand for plastic is on the rise. In developed countries, the average person uses 100 kilograms of plastic each year. It takes 500 to 1,000 years for plastic to disintegrate - meaning until then, it just keeps piling up.

Water is money

One other reason clean water is often the highest priority for development: The social and economic effects of not having a safe water supply are immense. These affect food, housing and health. Around the world, people spend hours each day collecting water when they could be working or studying. In economic terms, every $1 invested in water and sanitation has an economic return of up to $34.

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