The influence of geology on the quality of groundwater for domestic use: a Kenyan review.

Kenya's population, akin to other Sub-Saharan countries, is rapidly growing. With the increasing unreliability of surface water, groundwater resources are becoming highly relied on for domestic and industrial use. Despite several known contaminants reported in different parts of the country, no study has attempted to correlate groundwater quality in the different geological provinces. This review critically synthesizes the influence of Kenya's diverse geology on groundwater quality for human consumption. This was achieved through a review of published journal articles and other research material through research and government databases. Groundwater was categorised based on the major geological provinces including the Archaean volcanic Nyanzian Craton, the Proterozoic metamorphic Mozambique Mobile Belt (MMB) and volcanic Kisii Group, the Palaeozoic and Mesozoic sediments, and Tertiary volcanic Rift Valley. Groundwater quality in these regions showed a characteristic high concentration of fluoride (F^-) in volcanic aquifers of the Rift Valley and Nyazian Craton and metamorphic aquifers of the MMB, where mineral dissolution was the main process of F^- release. High salinity was common in metamorphic aquifers in the MMB and the Palaeozoic and Mesozoic sedimentary aquifers where mineral dissolution and seawater intrusion were the common contributors to salinity. Other contaminants such as lead and iron were reported in localised areas in the sedimentary and metamorphic aquifers, respectively. Anthropogenic contaminants such as Escherichia coli (E. coli), NO₃ ^-, and NO₂ ^- were common in shallow groundwater resources in most informal settlements in urban areas. Due to the presence of health implications, of the highlighted contaminants, such as fluorosis, high blood pressure and diarrhoea (due to high F^- and salinity) in affected regions, this review highlights the need for an active water resource management program in any country relying on groundwater resources to determine the presence of all region-specific potentially harmful chemical elements and mitigation measures in all its water resources.