India is urbanizing fast. As its cities expand, so more and more food is grown near built up areas – or even in conurbations themselves. For farmers of perishable produce like vegetables, production close to urban markets makes sense: Demand is year-round and freshness can be guaranteed. But the big drawback is access to land and water. Plots near cities quickly become expensive and water may be siphoned off for domestic and industrial use.
Using wastewater for agriculture
One way round this is to use city wastewater for crop irrigation. This has an added benefit in that wastewater is often high in nutrients so improves crop yield. In the summer season when freshwater is scarce and prices are high, wastewater may be the only cost-effective irrigation option for many growers.
With a population of just over 60 million, Karnataka is one of the most urbanized states of India. According to the Central Pollution Control Board, Karnataka generated over 3,700 MLD (million liters per day) of wastewater in 2015. However, sewage treatment capacity of the state is only 1,300 MLD which means that nearly 65 per cent of wastewater is discharged untreated into water bodies, deteriorating water quality.
Untreated wastewater often carries pathogens and other dangerous toxins, but many farmers continue to use this water for irrigation because it is the only source available to them.
So how do Karnataka farmers view the risks of using wastewater? A new study, recently published as apolicy brief by the IWMI-Tata Water Policy Research Program, sought to find out. Researchers surveyed famers around the cities of Hubli Dharwad and Vijayapura. In order to assess the costs and beneﬁts of wastewater irrigation, a representative sample of 43 farms was studied in detail. Twenty-six of the sample farms used wastewater while the remaining 16 used groundwater.
In general, the growers did not rank the health risks of using wastewater high. Nor, they claimed, have they ever received complaints about the quality of vegetables or other crops they produce. Despite using wastewater for the last 20 years, they did not report any deterioration in soil quality; rather that the productivity of land has improved over time. Yields in wastewater irrigated vegetables like cauliﬂower and ridge gourd in Hubli-Dharwad and beetroot in Vijayapura were reported as being nearly 20 per cent more than freshwater irrigated vegetables. On an average, freshwater farmers spent 3 times more on fertilizers than wastewater farmers.
So what are the health risks? The researchers noted that untreated city sewage eventually gathers in open drains (nallahs) and ﬂows into the city’s hinterland. During the ﬁeld visits, farmers were found to be developing methods to adapt to declining water quality in order to maintain or increase yields and minimize health problems.
Farming in urban areas of Kolkata
A very small proportion of farmers in both locations have started using settling tanks and ﬁlters before applying wastewater to their crops. These methods collect suspended solids from wastewater. The ﬁltration serves two purposes: it prevents debris from entering the pump thereby reducing wear and tear, and it prevents the fouling of soil with any debris and solid wastes present in the sewage. However, other wastewater users directly pump out the raw sewage and let it into the ﬁelds without any ﬁlter. This water often contains solid waste like plastic, used syringes and other rubbish, which could be hazardous both to consumers and to farmers.
In many countries “greywater” from domestic use is successfully used for irrigation. “Blackwater” – potentially harmful sewage – can also be safely used if simple guidelines are followed to minimise health risks. In the case of Karnataka only a few farmers seemed to be taking these precautions.
So what can be done? We need to move away from constructing more and more sewage treatment plants, say the report’s authors, and view municipal wastewater as a source of nutrients and water. Once it is positioned as a ‘resource’ and not ‘waste’, the focus can shift from disposal to recycling.
Stronger partnerships between municipal managers and farmers are needed to make wastewater application safer, says Alka Palrecha, one of the researchers. “Sieving and settling, use of safety boots and gloves, and reasonable crop restrictions could all help improve matters. For instance, if the retention period in settling tanks is sufficiently increased, the pathogen load of wastewater decreases considerably.
“Wastewater irrigation of green leafy vegetables should be completely avoided as they are short in height, require frequent plucking, and involve direct contact of farmers with wastewater. Non-food crops like cotton or flowers could be promoted to minimise potential health risks. If food crops are grown, they should be washed and properly cooked prior to consumption. Eating raw food grown with wastewater needs to be discouraged.”
Wastewater irrigation is a reality, say the authors, so banning it is not likely to be a practical option. A more effective approach will be to promote practices and policies that can ensure its safe use