Sand dams: providing clean water?

[Individual articles from the Winter 2019 issue of Intersections will be posted on this blog each week. The full issue can be found on MCC’s website.]

Located in the semi-arid region southeast of Nairobi, Kenya, the region known as Ukambani maintains a substantial maize-growing agricultural population. However, inconsistent and low rainfall presents challenges to providing enough water for crops, livestock and household usage. Communities and organizations have adapted by building thousands of sand dams and taking advantage of the region’s conditions (sandy soil, variable slopes and defined rainy and dry seasons) to harvest and store water in seasonal riverbeds for later use.

Part of the attraction of sand dams as a solution in this region lies in their purported ability to filter rainwater as it percolates through the sand pores, providing not only a consistent source of water, but one which is safe to drink. However, this is an assumption which had gone untested. Recently, MCC Kenya engaged with two partners, Utooni Development Organization (UDO) and Sahelian Solutions Foundation (SASOL), to test the water harvested from the sand dams to see if it was indeed clean and safe for drinking. Contrary to expectations, water from scoop holes had consistently high levels of fecal coliform bacteria. This finding spurred a recognition that additional efforts are needed to ensure safe use of water from sand dams. This experience with UDO and SASOL underscores the importance of rigorously testing assumptions about project effectiveness: doing so can reveal previously unrecognized conditions, which can then in turn spur action to achieve better project outcomes.

With a rapidly increasing population putting pressure on water supplies, sand dams can be an elegant and effective solution to providing water for communities in semi-arid regions such as Ukambani. The principles of sand dam function are conceptually simple to understand, and the results can be dramatic. Concrete dams constructed across seasonal streams cause coarse sand to accumulate behind the dam, and pore space in the dam then holds water which can be accessed by the community for many subsequent months of dry seasons.

In well-functioning dams, a patch of emerald green vegetation flourishes at the dam site well into the dry season, and visitors to the region can easily find examples of communities with thriving grasses and grain, vegetable gardens and orchards that depend on water from sand dams. A recent evaluation undertaken by MCC Kenya, in collaboration with UDO and SASOL, added to the body of evidence outlining the various benefits of accessing this water source. Community members identified benefits that varied dramatically with gender and age. Men and boys near sand dams stressed that water from sand dams was beneficial for brick-making. Girls, meanwhile, noted that better access to water allowed for better sanitation and hygiene, which in turn led to improved school attendance. Women, for their part, cited the benefits of reduced time needed to fetch water.

Sand can be an effective filter, and in fact sand filter technology is one of the WASH solutions widely adopted in WASH projects around the world. Water clearly does filter through the sand into scoop holes (simple holes in the sand, which are the most common method used by communities to access the water), suggesting that sand dams could provide a purifying role for the water held in the dams. With the help of a donation of bacterial testing materials from an MCC constituent with extensive experience in water testing, we went about testing this assumption. Kenyan partner staff and local university students received training in techniques needed to answer if sand dams do in fact purify water held in the dams. We then randomly selected sites from a list of existing dams and evaluated a combination of biophysical and social parameters related to water quality at each of these sites.

The results of this study were clear: 84% of dams in the dry season had more than 100 fecal coliform colonies per 100 ml. This is well above the World Health Organization standard for fecal coliforms (zero), and in the high- to very high-risk category. Surprisingly, it was not statistically different from surface water (nearby areas that had standing water on the stream or dam surface). These results were consistent with a study by another group in the region, which likewise found consistently high fecal coliform levels in scoop holes. Together, these studies point to a previously unrecognized health hazard.

Equipped with the knowledge that untreated water from sand dam scoop holes presents a health hazard, MCC and its partners have worked to identify potential solutions. One approach is to change the method of water harvesting by relying on sealed pump wells rather than scoop holes, a solution that had already been implemented by SASOL in some areas. Water from pump wells was in fact much cleaner on average, but still showed fecal coliform contamination in 25% of cases; this approach also suffers from well-known challenges of maintaining the pump wells.

For its part, UDO responded to the finding of contaminated scoop hole water by implementing a pilot water, sanitation and hygiene (WASH) program in three communities aimed at identifying locally appropriate approaches to improve health measures associated with water quality, including water purification. Over a one-year period, UDO staff worked with 177 households to offer training in and support for improved WASH facilities and practices. Some WASH behaviors did improve during this period, such as the percent of households practicing water treatment, which went from 31 to 76%.

Why would the water from sand dams not be clean? A quick perusal of the surface of sand dams gives the observer clues to this unexpected result—the area on and around most sand dams is usually littered with animal dung. While the intention at sand dams is to limit livestock access to water sources in order to avoid contamination, in practice this proves difficult to maintain, and the distance from animal dung to the scoop hole typically is not far. Although we could not specifically test whether dung was the source of the contamination, we hypothesize that contamination originates with this livestock, just as it does in waterways in Canada and the United States where livestock access is not controlled.

Perhaps more puzzling is the question of why it was assumed and reiterated by villagers and promoting organizations alike that water from sand dams was clean. Our survey of communities that utilize sand dams indicated that in 74% of communities, most or all believed that the water was clean, and in 71% of communities, most or all did not treat water before drinking. This does not imply people are willfully ignoring the problem, or that there is a lack of expertise on the part of villagers or organizations. It does point towards the power of narratives. Indeed, the assumption of clean water fit well into a narrative of sand dams providing multiple benefits that were well-suited to local conditions. The known effectiveness of sand filters also provided a powerful analogy, and it was logical to assume that sand dams would function in a like manner to these sand filters. These biases led to untested assumptions, and points to the importance of experimental investigations. By rigorously testing our assumptions about development projects, we can uncover areas where our biases and perceptions might lead us to erroneous conclusions.

Doug Graber Neufeld is professor of biology and director of the Center for Sustainable Climate Solutions at Eastern Mennonite University.

Learn More

Quinn, Ruth, Avis Orlando, Manon Decker, Alison Park and Sandy Cairncross. “An Assessment of the Microbiological Water Quality of Sand Dams in Southeastern Kenya.” Water 10 (2018): 708-722.

Kostyla, Caroline, Robert Bain, Ryan Cronk and Jamie Bartram. “Seasonal Variation of Fecal Contamination in Drinking Water Sources in Developing Countries: A Systematic Review.” The Science of the Total Environment 514 (May 1, 2015): 333-343.


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