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.

Sand Dams as a Potential Solution to Rural Water Security in Drylands: Existing Research and Future Opportunities

“…Total hardness levels should not exceed 300 ppm in drinking water WHO (2011). Moïse et al (2019) found mean TH to be 277.38 mg/L. Whilst a maximum hardness of 1,115 mg/L was recorded, 92% of samples complied with WHO recommendations.…”

“…The majority of papers found a similar proportion of samples falling below quality standards. All studies recorded some samples of high to very high risk, except for Moïse et al (2019) whose TDS samples all fell below 1,200 mg/L (marginal)indicating minimal risk. Quinn et al (2018a) tested EC at 50 dam sites with many pump wells and scoop holes tested twice, improving the reliability of results.…”

“…Although those selected sites were only from 1990 onwards and built exclusively by two sand dam organizations, bias is limited due to the random selection. Moïse et al (2019) on the other hand, purposively selected only three dam sites based on water availability, ease of accessibility and presence of at least two modes of abstraction. The very small sample size and selection criteria could explain the lower recorded values of TDS and could have introduced unconscious bias.…”

“…EC/TDS levels Borst and de Haas (2006) EC ranged from below 600 µS/cm in the rainy season to over 20,000 µS/cm in the dry season Kitheka (2016) EC ranged from 455 to 6,640 µS/cm in the dry season and 155.9-539 µS/cm in the rainy season Quinn et al (2018a) Of 83 samples, 25% measured EC above the WHO recommended limit of 1,500 µS/cm Chan (2019) Six of 29 samples from hand pumps recorded EC above the WHO recommended limits Moïse et al (2019) All samples recorded TDS of <1,200 mg/L Graber Neufeld et al (2020) Salt content from scoop holes, hand dug wells, pump wells, and surface water in the dry season was poor or unacceptable in 33% of samples E. coli ranged from <1 to 150 cfu/100 ml in shallow wells and from <1 to 300 cfu/100 ml in scoop holes. 87% of shallow well samples and only 48% of scoop hole samples complied with WHO guidelines for E. coli.…”

“…Other physicochemical quality parameters explored in the literature include turbidity, pH, temperature, total hardness (TH), biochemical oxygen demand (BOD), and trace metal elements. On analysis of these findings, turbidity is the most critical physicochemical parameter as turbid water is unpleasant to taste, difficult to chlorinate, and bacteria, viruses and other microbial parasites can hide themselves in the suspended particles (Moïse et al, 2019). It is recommend by WHO that turbidity should not exceed 5 NTU (WHO, 2017).…”