Water for All, Disease for Some?

Greater access to water for irrigation, sanitation, and household use is an oft-repeated goal of development agencies worldwide. The mantra states that the provision of water at the household and community level improves nutrition, social equity, and ultimately life spans and quality of life. But what happens when environmental interventions meant to lift communities and buffer against climate change have a negative impact on environmental health? One study provides a troubling view of the potential downsides of building new water retention structures.
 
Researchers from several African universities and research centers, as well as the International Water Management Institute, investigated the links between the development of water retention infrastructure, both large and small, and two particularly impactful water related diseases. Common measures of the impacts of disease are deaths and disability adjusted life years (DALYs), which describe the incremental loss in life quality and length due to disease. The better known, and more deadly, of the two diseases is malaria, the mosquito borne cause of nearly 31,000,000 DALYs in Africa alone; just less than half of the malaria worldwide impact and nearly 8% of all DALYs in Africa, where most of the 660,000 annual deaths occur[1]. The second water borne disease is schistosomiasis, a snail based parasite found in water bodies across the developing world. Although less widespread than malaria, 243 million people were exposed to schistosomiasis in 2011, causing 41,000 deaths globally in 2004, some 36,000 of which were in Sub-Saharan Africa.
 
Across numerous study sites in two countries, Burkina Faso for the investigation of schistosomiasis and Ethiopia for malaria, the investigators sampled water bodies behind built infrastructure for the presence of disease vectors, and the communities nearby for evidence of infection. In Burkina Faso, the density of host snails was found to have a "close relationship" with the both presence of small reservoirs as compared to natural stream and lake habitats and population centers, with nearby villages exhibiting up to 99% schisto prevalence. The studied reservoir pools contained twenty times more snail habitat than did the natural lakes, a troubling omen for a widespread adaptation technique. The study regions in Ethiopia spanned aquatic sites large and small in a diverse array of locations. Across all areas, the manmade bodies of water showed greater concentrations of mosquito larvae, and the incidence of the disease in the population was higher in those villages with harvesting ponds nearby to the homes. These findings strongly suggest a relationship between manmade water bodies and malaria risk.
 
What does this mean for the future of water retention investments in the face of climate change? The authors determined that groundwater recharge provides the greatest advantage vis a vis disease vectors but is not technically feasible everywhere. Covered storage, while relatively safe from disease, is difficult and cost prohibitive. In schistosomiasis endemic areas, the most prevalent snail host is highly adaptive to droughts and heat, creating a situation in which public health officials will have focus on either increasing treatment in communities or approaching an alternative strategy. The outlook for malaria control is more favorable, with several soft and hard management alternatives available. Promoting certain vegetation along the shallow shore areas can reduce the available breeding habitat for mosquitoes, as can manipulating water levels to disrupt breeding patterns. The slope of the shoreline can also impact mosquito habitat and reduce mosquito populations. When planners adopt a wider view of water storage, they may avail themselves of further alternatives. Partially buried storage can provide a balance between cost and disease control, and the use of natural wetlands for storage can expose disease vectors to predators and other environmental controls. Participatory processes in planning, design, and operation may further inform the most sustainable decisions for the location.
 
Options for disease control expand well beyond the type of retention infrastructure used. Sanitation improvements can reduce the Schistosoma parasites and sleeping under bed nets can help to break the transmission cycle of malaria, though these are independent of water retention decisions and are no regrets interventions even in the absence of water infrastructure. The most efficient water harvesting techniques to guard against climate change, however, are also those with the greatest potential to expand disease vectors. Perhaps the most important thing is that the full spectrum of both benefits and risks to any climate adaptation intervention are understood, including the potential costs and benefits to expanding engineered water storage, and the local capacity to manage any such interventions.

[1] http://www.who.int/mediacentre/factsheets/fs094/en/