Groundwater represents a vital source of freshwater to meet distributed, rapidly rising demands for safe drinking water, irrigation and industry in low-income countries across the tropics. The hydrochemistry of groundwater within deeply weathered crystalline rock aquifer systems that predominate at low latitudes, is determined primarily by long-term biogeochemical weathering of the parent bedrock. Here, we evaluate geochemical footprints and baseline chemical quality of groundwater that have developed from water-rock interactions across a range of geological environments in Uganda using a national database of hydrochemical and hydrogeological records from 3271 locations. Sampled groundwaters are mostly shallow (69% of samples from depths of <20 m below ground level), fresh at time of drilling (Electrical Conductivity <1000 μS cm−1 in 96% of samples), and of good quality (<8% of samples exceed WHO (2011) guidelines values for chemical parameters in drinking water). Unpalatably high concentrations of total soluble and suspended Fe are, however, common (21%) in meta-igneous, granitic and metamorphic formations. The dominant (95%) anionic facies of groundwater is bicarbonate (HCO3−), indicative of localized flow systems (i.e. discontinuous aquifers) in which chemical evolution of groundwater (e.g. as per Chebotarev sequence) is minimal. Low well yields (82% < 3.6 m3 h−1) and specific capacities (84% < 5 m2 d−1) support this inference; low aquifer transmissivities and storage serve to regulate naturally groundwater withdrawals (i.e. impacts of over-abstraction are localized). Overall, the results attest to the intrinsic high quality of groundwater that occurs in deeply weathered crystalline rock environments in Uganda, which may be expected across tropical Africa
