An intriguing new study is out on the use of wastewater in world agriculture. If you've ever wondered where all that cruddy old water goes when you pull the bathtub plug, brush your teeth, or purge the loo, this is the report you've been waiting for. The short answer: On your salad. The big surprise is, that may not be all bad.
In a survey of 53 cities worldwide, the International Water Management Institute (IMWI), a water research and advocacy group, has found that the vast majority of produce cultivated in urban plots is irrigated with what amounts to tainted water, fetched from polluted streams and lakes or wells. True, only a fraction (say 10 percent) of global agricultural output is harvested in the cities, and only a part of that crop is consumed uncooked. Yet in these cities alone, some 1.1 million farmers produce vegetables and fruit for 4.5 million people. Projecting the numbers worldwide, no fewer than 200 million farmers rely on recycled water to sow 20 million hectares, an area twice the size of Hungary. The findings were released during World Water Week, a summit of sages and policy types gathered in Stockholm through Aug. 23 in an effort to rethink the way the world farms and flushes.
At first whiff, this all seems dire. After all, the water we dump, from sink or commode, back into an ecosystem, carries a galaxy of bugs, bacteria and germs that can cause nasty diseases from diarrhea to hepatitis. Worse, it's a good bet that most families that consume the fruit and vegetables grown with such swill do not properly wash their produce, a sure invitation to illness. Cholera outbreaks in Israel and Chile have been traced to food contaminated with wastewater.
Now it turns out that even the plumbing has a silver lining. Noisome as it seems, dirty water may be the only reason that many people around the world eat at all, especially in the poorest countries. Nearly 200,000 residents in Accra, the capital of Ghana, put produce on the table thanks largely to wastewater. Nearly a quarter of Pakistan's domestic vegetables are nurtured with wastewater. It's no exaggeration to say that "bad" water helps fill the bowls of scores of calorie depleted households around the world.
Add to that the fact that irrigating with waste adds a kind of pro bono fertilizer to the farm and also returns moisture to drying lands. "It's a great way to cope with water stress," says senior IWMI official, Pay Drechsel. The soil is also a great natural filter, "cleansing" dirty water as it seeps into the ground. There may even be a plus for the climate, as sludge-laden water returns carbon to the earth that would otherwise be released into the atmosphere.
More to the point, there may be little alternative. For a time, the World Health Organization, rightly fearing the rampant spread of diseases, cautioned against using tainted water for cropping. But in time, "they realized this would put millions of farmers out of business," says Drechsel. Some 85 percent of the 53 cities studied dump their sewage and wastewater into streams and lakes. In the poorest societies, where clean water is as precious as it is scarce, diverting fresh water to the farm is to rob the drinking glass.
WHO has now adapted its approach, signing off on farming with wastewater in countries where clean water is scarce but with the caveat that authorities move aggressively to treat waste and that families thoroughly wash their produce. "With an ever greater number of emerging economies lacking resources to adequately treat their waste, this situation will continue."
So pull the plug and pass the salad. But wash, first.