Groundwater quality constrains and new opportunities for water supply from hard rock aquifers in a fast-expanding city of Sub-Saharan Africa, Yaoundé-Cameroon

Expanding cities and their water utilities face a significant challenge ensuring safe and sufficient water supply within a context of great uncertainty. Population growth, urbanisation and economic fluctuation coupled with climate variability further exacerbate these problems in Sub-Saharan Africa (SSA).The study focusing in Yaoundé-Cameroon, Central Africa demonstrates quality constrains and new opportunities of water supply from hard rock aquifers. Stable isotopes and hydrochemical parameters of 56 boreholes, 57 dug wells, 31 springs and 22 rivers, sampled in the dry and wet seasons were used to provide visibility of the groundwater system in addition to its interaction with surface water. Stable isotope results of δ18O and δ2H show uniform mixing of the groundwater masses from rainwater infiltration. Groundwater chemical compositions show variable mineralisation, linked to the environment in which water circulates and the land use change, reflecting classical polluted NaK–NO3 urban groundwater type and CaMg–HCO3 natural water quality in the peri-urban area. The enriched shallow urban groundwater is further reflected in surface water indicating interaction of the two water masses. Hydrochemical processes reveal pollution constrains in urban groundwater uses and the importance of rock-water interaction and residence time in the peri-urban groundwater. The defined NBL/TV coupled with the new water supply scheme could be helpful in the land use management practices, monitoring of the natural water quality and improving access to safe drinking water in SSA.