Kolkata’s fishermen and farmers reuse what’s flushed down the toilet

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March 2017 : Most people don’t think about what happens to their excreta when they flush the toilet or pour water down the latrine. But, for fisherman and farmers in Kolkata, India, excreta provides a natural fertilizer for their crops, food for their fish and an income to provide for their families.

A man bends over to pick bushes in fields irrigated by reused wastewater in Kolkata, India


For more than a century, Kolkata’s underground sewer system has been pumping untreated wastewater into more than 250 ponds on 12 000 hectares of land in the East Kolkata Wetlands.

Through sunlight and oxygen, human sewage is converted into plankton and then consumed by fish that are grown and sold in the local market. The pond water is then channelled to irrigation ditches and used to grow vegetables, such as carrots, radishes and onions.

Kolkata’s wastewater reuse system, the largest in the world, recycles almost 90% of the city’s waste for aquaculture and agriculture. The fish and crops grown provide an income for more than 20 000 families who work in the area.

“Through reusing the wastewater, Kolkata’s farmers and fishermen are not only helping reduce water and soil pollution, but also contribute to nutrition of the city’s residents. But this practice has health risks – like diarrhoea or helminthic infections – on the farmers themselves and downstream communities,” says Payden, sanitation engineer at WHO South-East Asia Regional Office.

“The challenge now is ensuring wastewater is treated and reused safely.”

Safe wastewater reuse ever as important as fresh water supplies diminish

Worldwide, as water resources become scarce, urban centres expand and demand for food increases, wastewater reuse is becoming more attractive and viable. Today, it is estimated that more than 10% of the world’s population consumes food produced with wastewater and 40% live in water-stressed areas.

However, wastewater treatment is low in most developing countries, posing various risks to human health from diarrhoea, cholera, typhoid and worms. Untreated and poorly managed wastewater also helps spread antibiotic-resistant bacteria when it used for bathing, drinking-water or growing food.

“At any given time, nearly half the developing world’s population is affected by an illness or disease directly linked to unsafe water, inadequate sanitation or poor management of water resources,” says Dr Henk Bekedam, WHO Representative to India.

In 2014, WHO estimated that moving from no sanitation to improved sanitation only reduces diarrhoea by 16%; however, when excreta is properly removed from households, treated and safely disposed, an additional 63% reduction in diarrhoea results.

Sustainable Development Goals target safe sanitation management

To help countries safely treat, manage and reuse wastewater, WHO developed the Sanitation Safety Planning (SSP) a risk management tool in 2016. The tool helps sanitation operators apply WHO’s Guidelines for safe use of wastewater, excreta and greywater in agriculture and aquaculture and identify and manage the health risks along the sanitation chain. The multi-barrier approach used means risk can be reduced through simple measure even when expensive treatment is not feasible in the short term.

Last year, WHO provided SSP training to 34 participants from 6 countries in the South-East Asia Region in order to create regional champions who could further support countries to safely manage their sanitation systems. To learn how to identify risks in sanitation systems, the participants visited the East Kolkata Wetlands and interviewed farmers in the area.

WHO is now conducting a risk-assessment of the East Kolkata Wetlands utilizing the guidelines and SSP tool to help the city understand how to improve the system and reduce health risks to both fishermen and farmers who live in the area, as well as the wider community consuming the fish and vegetables produced.

While the Millennium Development Goals (MDGs) improved access to safe water and sanitation, they did not focus on ensuring excreta was properly removed from households, treated and safely disposed.

The Sustainable Development Goals (SDGs) are now focusing not only on improving access to safe water and sanitation but specifically calling for safely managed sanitation and increased treatment and safe use of wastewater. Through SSP, WHO is working with countries to ensure proper collection, transport, treatment and safe reuse or disposal of faecal matter along the sanitation chain.

“Ensuring the availability and sustainable management of water and sanitation for all impacts not only health outcomes but also has positive linkages with combating climate change and fighting poverty,” says Dr Bekedam.