Irrigation is the primary agricultural use of human waste in the developing world. But frequently untreated human feces harvested from latrines is delivered to farms and spread as fertilizer.
In most cases, the excrement is used on cereal or grain crops, which are eventually cooked, minimizing the risk of transmitting water-borne pathogens and diseases, IWMI's Drechsel noted.
With fertilizer prices jumping nearly 50 percent per metric ton over the last year in some places, human waste is an attractive, and often necessary, alternative, Redwood said.
In cases where sewage sludge is used, expensive chemical fertilizer use can be avoided, he said. The sludge contains the same critical nutrients—nitrogen, phosphorous, and potassium.
It is generally unheard of for untreated wastewater to be used for agriculture in developed countries, simply because farmers there have access to treated water, said Margaret Catley-Carlson of the Global Water Partnership.
Instead, farmers in developed countries use recycled wastewater that often meets drinking-water standards.
To address health risks associated with wastewater agriculture in developing countries, IWMI recommends education programs for both consumers and farmers.
The nonprofit also recommends that such operations adhere to World Health Organization (WHO) standards for safe wastewater usage. WHO, in turn, has made their own standards less stringent.
"Overly strict standards often fail," James Bartram, a WHO water-health expert, said. "We need to accept that across much of the planet, waste with little or no treatment will be applied to agriculture for good reason." According to IWMI's report, few developing countries have official guidelines for the use of wastewater for farming. But the fact that authorities are even acknowledging that wastewater agriculture exists is progress, the report says.
In the city of Kumasi, Ghana, home to 1.6 million people, IWMI estimates that there are about 12,000 families growing food on 27,000 acres (12,000 hectares) using mostly polluted surface water.
Just this year the Ghanaian government began to recognize this type of informal irrigation in its new irrigation policy, according to IWMI's Drechsel, who views the move as a giant breakthrough for addressing related health issues.
There are also low-tech solutions for "treating" human waste. IWMI suggests employing appropriate and time-tested indigenous practices.
The report cites examples in Indonesia, Nepal, and Vietnam. There, farmers store wastewater in ponds to allow solid feces and worm eggs to settle, possibly reducing bacterial content in the residual water.
Composting, in which heat kills much of the bacteria, is another option, according to the report.
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