Is your food watered by waste?

Our food supply is more vulnerable to pollution than we thought.

Children play on cement sewer pipes near a construction site in Ahmedabad
Children play on cement sewer pipes near a construction site in India [Amit Dave/Reuters]

New research out this week suggests that the possibility of our food being contaminated by waste water is higher than we ever thought. In fact, around 885 million of us (that’s almost one in nine) are at risk of consuming foods that have been irrigated by wastewater.

As cities spread and populations steadily expand, water treatment facilities and food safety procedures are not keeping pace in low- and middle-income countries. The new study is the first to use geospatial analysis to assess the extent to which wastewater is used in agriculture (either raw or diluted, treated or untreated), and reveals the practice is at least 50 percent more common than earlier available estimates. Previous estimations had relied on isolated case studies, guesswork and methods that were not easily comparable – but we now have a much more accurate, global picture of the problem.

It is hardly surprising that poor farmers, particularly in water-scarce and food-insecure regions, are turning to this readily available resource to protect their livelihoods and ensure that communities are fed. Moreover, where wastewater is largely undiluted, it has a high concentration of nutrients that will enable farmers to reduce or eliminate the amount of fertiliser they otherwise need to purchase.

But this comes at a cost. Wastewater is usually contaminated with varying levels of excreta-borne pathogens, which put not only farmers but also consumers at health risk, especially where irrigated crops, like certain vegetables, are eaten raw. The wastewater irrigation pathway can become an infection highway, leading to intestinal infestation with parasitic worms, diarrhoea and even potential outbreaks of cholera.

Several geographic regions have been exposed by the new study as major hotspots for unsafe wastewater reuse in agriculture, raising a red flag for public health in these places. In India, for example, 8.9 mega hectares of land are irrigated downstream of cities with a high likelihood of untreated wastewater – this account for about 15 percent of India’s irrigated land. Research shows more than 80 percent of the pathogenic pollution of surface water in India has been attributed to the approximately 100 million septic tanks and 60 million latrines in urban areas, which are poorly maintained, and lack treatment facilities for the captured excreta. This results in human waste continuously finding its way into water bodies and potentially the food system.

READ MORE: More than half a billion globally ‘have no clean water’

It is clear we must step up our response to this problem, in order to reduce the risks, particularly for the poor. We recommend a dual line of response.

Gaining a better grasp of how business solutions can be replicated will be an important step towards turning the global wastewater challenge into an opportunity.


Reducing the risks of wastewater use for farmers and consumers in the short term requires a “multi-barrier” approach, as recommended by the World Health Organization (WHO) – especially for situations where we cannot yet rely on comprehensive wastewater collection and treatment. This approach consists of a series of actions that fight contamination along the entire food chain. These include wastewater treatment (if available), but focus strongly on safe irrigation, as well as hygienic food handling and preparation. These on-farm and post-harvest actions can jointly reduce the disease burden by 70 percent, if only three out of four farmers, traders and households adopt the recommended practices.

Sadly, behaviour change needs time. This is due to a number of reasons – from lack of consumer awareness about the health threat to farmers’ limited (financial) incentives to change their practices, as well as low institutional capacities to support regulations.

Yet there also exists an opportunity to turn the entire wastewater challenge on its head – and to see this abundant resource as an asset instead of a threat. This involves focusing on the vast number of septic tanks and pit latrines which capture around 90 percent of wastewater in many low- and middle-income countries. With the right investments, the collected faecal sludge can provide us with valuable by-products, from fertiliser to power. It is estimated that the global wastewater supply could generate enough energy to provide electricity from biogas for about 130 million households. And where biogas technology faces challenges, the sludge can be easily dried and pressed into briquettes, a practice increasingly seen in East Africa.

WATCH: ‘Flying toilets’, waste and biogas in Kibera (2:56)

If businesses can tap into this opportunity, then overflowing septic tanks will become history and the costs of excreta treatment could be recovered through the sale of valuable products. This will provide the necessary incentives to catalyse sustainable wastewater management beyond the provision of toilets.

In Ghana, this step change is taking shape. A recently launched co-composting plant in Greater Accra will produce and market 500 tonnes of a new organic fertiliser named, Fortifer, annually, by treating 12,500 cubic metres of human waste, and 700 tonnes of other organic waste. It is a safe, odourless, nutrient-rich compost, which the plant will sell in powder and pellet forms to improve the yields of common grains, like maize and rice, as well as any other crops. Fortifer received governmental approval and will not only bring incentives into the sanitation service chain, but also combat poor soil health which remains a major barrier to farm productivity and food security in Africa. The plant in Ghana has been set up as a public-private partnership, facilitated by International Water Management Institute.

Allowing water-borne health risks to enter the food chain could export local risks to global markets. Gaining a better grasp of how business solutions can be replicated will be an important step towards turning the global wastewater challenge into an opportunity. We must work together to tackle the root causes of this phenomena and protect the health of growers and consumers alike. 

Dr Pay Drechsel leads research on rural-urban linkages at the International Water Management Institute (IWMI) and the CGIAR Research Program on Water, Land and Ecosystems (WLE).

The views expressed in this article are the author’s own and do not necessarily reflect Al Jazeera’s editorial policy.