Assessment of drinking water quality, heavy metal pollution, ecological and human health risks in Kenya’s rural wetlands

Abstract This study evaluated spatiotemporal variations in drinking water quality, pollution levels, and heavy metal contamination in key rural water sources including, 23 dams, eight minor lakes, and three swamps. A total of 26 and 34 water samples were collected during the dry and wet seasons, respectively, and analyzed for ammonia, pH, nitrates, iron, manganese, zinc, copper, boron, chloride, fluoride, molybdenum, phosphorus, electrical conductivity, and water hardness. These parameters were used to compute the drinking Water Quality Index (dWQI) and Nemerow Integrated Pollution Index (NIPI). Additionally, 24 and 27 sediment samples were collected during the dry and wet seasons, respectively, and analyzed for heavy metals arsenic, chromium, cobalt, nickel, molybdenum, and lead using Inductively Coupled Plasma Optical Emission Spectroscopy. Results showed generally low heavy metal concentrations in water; however, isolated exceedances of WHO guideline values for fluoride, ammonia, manganese, and phosphorus were recorded in Lake Simbi Nyaima, Lake Solai, and Maruba Dam. The dWQI classified 84.6 and 85.3% of the sites as having excellent water quality during the dry and wet seasons, respectively, likely reflecting low rural population density and limited urban activities. However, most sites exhibited moderate heavy metal pollution in sediments based on NIPI. Nevertheless, the Potential Ecological Risk Index (PERI), Total Risk Index (TRI), and Hazard Quotients (HQ) indicated low ecological risk and no potential risks to aquatic organisms or human health. Multivariate analysis identified natural and agricultural activities as probable nutrients and heavy metal sources. These findings highlight rural wetlands as safe drinking water sources in Kenya.