No water to waste, not even wastewater
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Keraita, Bernard. 2002. No water to waste, not even wastewater. Spore 101. CTA, Wageningen, The Netherlands.
Permanent link to this item: http://hdl.handle.net/10568/47746
Internet URL: http://spore.cta.int/images/stories/pdf/old/spore101.pdf
With competition stiff for high quality fresh water for domestic and industrial users, the use of wastewater for agriculture can release better quality water for these other sectors. Wastewater unquestionably contains valuable nutrients, but poses...
With competition stiff for high quality fresh water for domestic and industrial users, the use of wastewater for agriculture can release better quality water for these other sectors. Wastewater unquestionably contains valuable nutrients, but poses health risks too. A look at the nuances. Wastewater irrigation is a reality. Though generally unacceptable, irrigation using untreated wastewater exists and is practised in many ACP countries, where sanitation and treatment infrastructures are poorly developed and, besides, are not a priority. A senior government water engineer here in Ghana once told me, 'The first priority is clean drinking water for all, then we shall think of wastewater.' Worldwide, 20 million hectares are reportedly under wastewater irrigation, but it is much more if we consider seasonal users who use it during the dry seasons, and those who use it in diluted forms from streams or rivers. Wastewater is basically the liquid waste suspended in water, mixed with groundwater or surface water. The main sources of wastewater are domestic and industrial. As a general rule, 80 85% of water used is wasted. Most populations in ACP towns and cities have outpaced the sanitation facilities, if these facilities are present in the first place. I am not opposed to treatment the technologies are there, ranging from the more complex trickling filters to simple ones, such as using duck weed and stabilisation ponds but if I just take the cases of Ghana and Kenya at a glance, then treatment will solve only a very small part of this wastewater problem. It is going to be a long-term exercise. A do or die situation In Accra, Ghana, the local authorities enacted a bye-law in 1995 prohibiting the use of untreated wastewater in irrigation, but today, 7 years on, farmers are still using it. It is a 'do or die' situation. I know the risks of wastewater use, but stopping it is very impractical. A major advantage of using wastewater is that it contains high levels of nutrients, reducing the need for and cost of fertilisers. Consequently, many farmers using wastewater are better able to support themselves and their families and often create extra employment. In addition, many of these people are poor, small-scale farmers living on the fringes of towns and cities and I say, if we are aiming at poverty alleviation, this is the group that we have to focus on. If alternative sources of water are not available, which is usually the case, we have to do more research to come up with better strategies to reduce the negative impacts while they continue using untreated water. The main constraint that often overshadows the benefits of wastewater irrigation is its negative public health image because of its contaminant constituents, such as heavy metals and microbiological pathogens. But in most ACP countries with limited manufacturing industry, heavy metals are not a major problem. The great worry in these countries is crop contamination from microbiological pathogens, including Escherichia coli bacteria and helminths that cause dysentery and diarrhoea. Few farmers wear protective clothing while irrigating, due partly to lack of awareness and partly to lack of money to buy the gear. Here in Ghana it is fairly common to see a farmer eating while irrigating. This exposure can cause diseases and skin-related infections. Farmers should be trained to avoid these problems. Without playing it down, I personally believe that the health issue is being exaggerated somewhat. Most research on this subject has focused on negative impacts on health rather than on positive impacts on food provision. This has led to an unbalanced impression among policy-makers who have gone ahead to make bye-laws that are against wastewater use. In turn, this has created distorted perceptions in public opinion. People claim that wastewater use in irrigation causes malaria, cholera, leprosy and so on. But this is not necessarily the case; these problems could stem from other farm activities or inputs such as manure. Besides, crop contamination can occur just as easily at market and consumer levels. We really have to do more research to clearly point out the actual effects of wastewater irrigation and their implications for both health and food security. Raw or cooked Nonetheless, several management practices can be implemented to reduce the negative effects. Instead of using overhead irrigation methods such as watering cans and sprinklers, applying water directly to plant roots is more appropriate, since soils and crops act as living bio filters. Furthermore, most pathogens die in 15 30 days, so if irrigation can be stopped well before the crops are harvested, then part of the risk can be reduced. The impacts of wastewater irrigation on crops that are eaten raw, such as lettuce or tomatoes, are likely to pose greater health risks than crops that are cooked before eaten. If crops are cooked well, most pathogens die at less than 60°C. In short, I have every reason to believe that wastewater irrigation will expand in the near future. With lower levels of treatment required compared to fresh water for consumption, it must be possible to use wastewater safely in agriculture. But we need to make policy-makers, donors and all stakeholders aware that this is a real need and that we are short of alternatives. [caption to illustration] Born in Kenya, Bernard Keraita is an irrigation and water engineer. He currently works with the International Water Management Institute (IWMI) in its Ghana office, where he coordinates the Wastewater Use in Agriculture Research project that covers the West African region. The opinions expressed in Viewpoint are those of the authors, and do not necessarily reflect the views of CTA.