Does the soil cleanse wastewater well enough to use on food crops?

Using waste water on food crops in developed nations is something very few people do. Besides the ‘ick’ factor and prospect of poisoning ourselves with viral diseases, the smell is usually enough to keep us from doing it. Our government does do a fairly good job of treating our waste water so that contaminated food does not end up in supermarkets, farmers markets, etc. It’s the handling of food after treatment is where the issue of food safety is problematic.

But in developing nations, recent findings by the International Water Management Institute (IWMI) found that 85% of cities discharged the water without any appropriate treatment. The root of the problem is pretty basic, cities are growing faster than waste water treatment plants can be built. In the conversion from a farming based society to an urban one, More and more farms are going to be needed to feed those people who don’t raise their own food. Since the flow of water is being directed more and more towards cities, those people who remain on farmland are being faced with waste water as their only water source.

A study, based on case studies from 53 cities in developing nations, examined where waste water was being generated, how much was being used in urban agriculture, and to what degree the water was being treated. "We know that there is an informal sector within many cities that is using [waste water] to grow vegetables, but there has been no data on how much of this water was being used or what the risks were," explained IWMI director general Colin Chartres.

The study’s authors highlighted a number of benefits of using wastewater to irrigate crops such as allowing food production in places where there was a lack of water, or where no alternative clean water sources were available, it also recycles nutrients, meaning that farmers did not have to buy expensive fertilizers.

The environmental benefit is that if the water just went straight into a river, it would cause a lot more eutrophication problems further downstream by increasing plant growth in lakes and streams that then die off and depletes the oxygen supply leading to the death of fish and other aquatic life. See ‘Dead Zones’ for an extreme example of this.

The real issue here is whether or not pouring waste water onto the soil surrounding food crops is healthy. Does the soil act as an effective filter to keep harmful human-based, disease-causing organism out of the food supply?

Allowing waste water to settle in a pond is a good sound alternative to chemically treating waste water and can therefore produce usable water. It still may not be clean enough to drink but for food crops I would say go for it. When the crop is harvested it stills needs to be washed with fresh, clean water. But if you don’t have access to fresh, clean water what are you to do?

 settle in a pond

Currently, farmers in developing nations conduct a smell test or a taste test and if the water tastes too foul or smells too bad, then they won't use it to irrigate their crops. Relying on smell and taste is not good enough.

IWMI is focusing on wetlands and pipelines to turn the tide on waste water usage in developing nations.