Abstract:
Makueni County is located in the semi-arid south-eastern Kenya region characterized
by unreliable rainfall and limited surface water resources. This necessitates a high reliance on
groundwater for domestic and agricultural use. In this paper, we report on the physico-chemical
characteristics of 20 drinking water sources (boreholes, shallow wells, streams, and tap water) collected
during the dry season (November 2018), the geochemical processes controlling their composition, and
their suitability for drinking water and irrigation. Of all the physico-chemical parameters analysed,
the concentrations of total dissolved solids, hardness, electrical conductivity, magnesium, calcium,
chloride, and fluoride exceeded the permissible drinking water limits set by both the World Health
Organization (WHO) and Kenya Bureau of Standards (KEBS) in up to 55% of the samples. The
dominant ions reflect the high salinity in the water that ranged from very high to extreme in up to
50% of samples. The northern region shows the highest concentrations of the dominant parameters.
The water type is predominantly Ca-Mg-HCO3 with a trend to Ca-Mg-Cl-SO4. Rock weathering and
evaporation are suggested to be the primary controls of groundwater geochemical characteristics.
High salinity and fluoride, which are associated with reported undesirable taste and gastrointestinal
upsets, as well as cases of dental fluorosis are some of the effects of consuming groundwater in
the region. These two parameters can be attributed to the weathering of biotite gneisses, granitoid
gneisses, migmatites, and basaltic rocks that occur in the area. The high salinity and alkalinity of
most of the samples analysed, renders the water unsuitable for irrigation in the study area.
