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.