What is wastewater agriculture?

­Imagine the end of a sewer line opening up onto acres of vegetable crops that will feed hundreds or thousands of people. And now, imagine that this is a good thing.

The fact is, in many poverty-stricken parts of the world, without wastewater irrigation hunger would be a much bigger problem than it already is. Wastewater farming solves several problems faced by these farming communities, primarily an inability to treat dirty water, prohibitively expensive chemical fertilizers and drought conditions.

The world is facing the greatest water shortage in history and the most severe food shortage in three decades [source: TD]. In cities where treating water to typical drinking standards is simply not an option, growing food using dirty water is an acceptable practice considering the alternative. It's becoming even more than acceptable, in fact: The price of chemical fertilizer increased 50 percent in some parts of the world in 2008 alone [source: Eichenseher]. The naturally occurring nutrients in sewer water act as a very effective, very cheap replacement. Vegetables respond especially well to the potassium, nitrogen and phosphorous in sewage, the same ingredients in chemical fertilizers. Wastewater might be pumped onto crop lands from polluted lakes, or raw sewage might be trucked in from dumping facilities to use as fertilizer. In especially desperate areas, farmers might crack open sewer lines and let the wastewater flood right onto the cropland.

If there's time, though, the water might be treated using simple indigenous methods. In some areas of Vietnam, Indonesia and Nepal, for instance, farmers create ponds of wastewater and let it sit until some of the pollutants (mostly feces and worm eggs) sink to the bottom, and then they apply the water to the crops. This water is much healthier than the raw stuff. Another cheap water-treatment method involves running it through composting sites. The heat from composting kills a lot of bacteria (see How Composting Works to learn more).

­Even with these minimal treatments, though, the water still carries a lot of bacteria and even some dangerous heavy metals. The consequences of widespread wastewater irrigation, even while saving entire cities from starvation, can be dire.

­Wastewater farming causes health problems to everyone involved in the process. It's not just the people who eat the food who are exposed to contaminated water. The farmers who use it to irrigate their land are even more at risk than the end consumers.

While bacteria are a serious health threat, the biggest health issue associated with wastewater irrigation is intestinal parasites [source: Ensink]. The World Health Organization (WHO) has determined that one intestinal-worm ovum per liter of water is fine for agricultural applications [source: Ensink]. Researchers found 28 ova per liter on average in minimally treated wastewater (using the pond-settling method, for instance), responsible mostly for roundworm infection. They also were able to identify up to 150 ova per liter in untreated water, leading to a high incidence of roundworm, hookworm and whipworm [source: Ensink]. In severe cases, these parasites can end up killing their host.

Another big problem associated with wastewater irrigation is land and water pollution. Bacteria in the food and water supply can become a permanent, widespread problem when the wastewater poured over cropland contaminates otherwise safe ground water and surface water used for drinking.

Despite these risks, both the International Water Management Institute and the WHO believe the benefits of wastewater farming far outweigh the drawbacks [source: Eichenseher]. Without it, more farmers in developing countries would have no income, and more people would have no food. But these world organizations do have recommendations for making the practice safer than it is right now.

First, it would help if more local farmers adopted indigenous water-treatment methods like pond-settling and composting. Another healthier practice would be limiting wastewater irrigation to use in crops that will ultimately be cooked by the consumer, like rice and other grains. A lot of this depends on education, which is ultimately the way wastewater health issues will have to be addressed, since in most cases, fully treating the water just isn't an option. While most of the farmers who have to use wastewater know it's unhealthy, they may not know about ways to affordably limit the risk. Widespread efforts to educate indigenous populations about simple treatment methods and safer crop choices may help decrease the dangers faced by the 10 percent of the world that relies on wastewater crops for sustenance.

And what about the other 90 percent of the world?

Since so much produce moves around the world, there is always the possibility of being exposed to produce irrigated with wastewater, even if you live in a developed country with high water standards. In the United States, for example, many vegetables are imported from Mexico, and many areas in Mexico don't treat wastewater before it floods into rivers -- rivers that will be used to irrigate crops [source: Bowen].

The best way, then, to avoid the dangers associated with wastewater agriculture is also one of the best ways to cut back on energy costs associated with food production: Eat local. It could end up saving you a lot more than money.

For more information on wastewater agriculture and related topics, take a look at the links on the next page.