Evaluation of sand-dam water quality and its suitability for domestic use in arid and semi-arid environments: A case study of Kitui-West Sub-County, Kenya

Abstract

Sand dams are one of the most successful rainwater harvesting methods, adopted in most of arid and semi-arid lands (ASALs) of Kenya to secure domestic water supply and micro-irrigation. Their ability to maintain acceptable water quality, under extreme climatic conditions of recurrent drought and floods, is therefore of paramount public health concern as various pollutants find easily their way into them. This study assessed the suitability of sand-dam water abstracted via scoop holes (SCHs) and shallow wells (SHWs) in Kitui-West, South-Eastern Kenya. Water quality compliance checks were performed using the specifications of Kenya Bureau of Standards (KEBS) for natural potable water and World Health Organization s (WHO) drinking-water quality guidelines wherever applicable. A total of 48 water samples comprising SCHs (N=33) and SHWs (N=15) were collected during the dry period (February 8 and 28, 2018) and the wet season (March 23, April 20 and May 19, 2018) in three sand dams using well-cleaned plastic bottles, transported in cooler boxes to the laboratory for storage and analysis. They were analyzed for pH, temperature, total dissolved solids (TDS), total hardness (TH), biochemical oxygen demand (BOD), trace metals (Cu, Fe, Mn, Zn, and Cr), Escherichia coli (E. coli) and total coliforms (TCs). Results showed that majority of assessed physicochemical parameters and trace metals complied with KEBS limits at the rates of more than 90% except turbidity, Cu and Fe that complied with low overall scores; 44, 56 and 35% respectively. These three parameters behaved differently in both abstraction methods as their mean values (compliance rates) exceeded KEBS limits in SCHs, that is, 297 NTU (18%), 1.7 mg/L (48%) and 2.22 mg/L (9%) and were below limits in SHWs, that is, 3.1 NTU (100%), 0.89 mg/L (73%) and 0.21 mg/L (87%) respectively. E.coli compliance levels were 48% in SCHs and 87% in SHWs with maximum counts as 300 CFU/100 ml, while TCs were detected at high rates of 94 and 47% respectively with maximum counts as 2,500 CFU/100 ml. Therefore, these results demonstrated that water extracted via SCHs is more unsafe than water from SHWs but both provide water that is microbiologically unfit for direct human consumption. Shallow-well water was found to be physicochemically fit and only requires disinfection while scooped water needs first to be purified with homemade water filters and then chlorinated with available disinfection by-products (DBPs) to increase its potability. Continuous monitoring of sand-dam water quality is recommended so that the public awareness should be raised on time when new contaminants emerge or exiting ones become intense so as to avoid possible health risks that can result from unnoticed long-term exposure. \n \n Key words: Sand storage dams, traditional scoop holes, offset shallow wells, drinking water quality compliance, natural potable water; physicochemical properties, organic matter, microbial pollutants, trace metals, climatic seasons.