Urban groundwater quality in Africa : benefits and challenges

Most urban centres in Africa rely on groundwater, in Southern Africa it is estimated that at least 36% of the population relies on groundwater, this number is much larger for many other settlements in Africa. Urban water supplies are reliant on local groundwater sources to supply 25% of water use, from both private and public/municipal sources. Groundwater is important even in areas where groundwater abstraction is limited by low productivity groundwater stores such as those found in hard-rock settings (e.g. granites). Urban centres are a focus for a wide range of human activities past and present that can alter groundwater quality with potential impacts on subsequent groundwater uses. Once contaminated, groundwater can be challenging to clean up. Despite these challenges, groundwater is often of better quality compared to surface water alternatives in urban settings. Groundwater is generally well protected from surface contamination: as water percolates through the soil and deeper rock some contaminants (e.g. bacteria) may be removed. In contrast to surface water pollution, groundwater quality changes are often gradual, allowing scope for the problem to be assessed and interventions and adaptations to be planned and undertaken if recognised early. Even when groundwater is contaminated (e.g. by bacteria or organic contaminants) these are often detected at low concentrations. Compared to surface waters treatment, costs are often lower and simpler treatment solutions are possible due to the reduced pollution loads and fluctuations in groundwaters. Access to groundwater is widely dispersed compared to alternative sources (lakes, rivers and piped supplies). This offers a clear potential to expand groundwater use in many towns and cities to enhance water security (e.g. via public water supply, piped systems with standpipes, self-supply such as private wells and in some cases tankered or sachet groundwater).