Performance evaluation of sand dams as a rural rainwater conservation and domestic water supply technology in East-African drylands, a case-study from South-Eastern Kenya

Sand dams (SDs) are rainwater harvesting methods in East-African drylands for rural water supplies and small-scale irrigation practices. However, little information exists on their ability to maintain the harvested water in the right quantity and quality. Three SDs were selected from south-eastern Kenya’s semi-arid zone as a case study to evaluate their operational performance. Water and sediment samples were collected and analyzed in both the field and laboratory. Six performance indicators, namely stormwater-capture efficiency (SCE), water-saving efficiency (WSE), volume-based and time-based reliabilities, water demand satisfaction rate (WDSR), water loss percentage, physicochemical water pollution index (WPI) and microbial non-compliance rate (NCR), were computed. Results showed that water storage in SDs is quite low and unfit for direct human consumption. In fact, three experimental SDs harvested 7,356 m3 during the long-rains season (March–May 2018) for an estimated water demand of 8,990 m3 (June–September). About 4,505 m3 (61.24%) was lost through evaporation (64.11%) and seepage (35.89%). These SDs exhibited low WDSR (31.72%), inadequate SCE (3.09%), low WSE (30.85%), dismal volume reliability (24.56%), and undependable time reliability (24.91%). Shallow-well water was less polluted than scoop-hole water but both didn’t meet the bacterial water quality standard (0 CFU/100 mL). The former scored a low WPI of 1.86 (reasonably clean) compared to clean water (WPI ≤ 1), while the latter scored a high WPI of 12.91 (considerably polluted). Furthermore, NCRs for total coliforms were 60% in shallow wells and 90.79% in scoop holes. Therefore, this water should be treated and disinfected for domestic use.