Urban groundwater quality in sub-Saharan Africa: current status and implications for water security and public health

Hydrogeol J (2017) 25:1093–1116 DOI 10.1007/s10040-016-1516-6 PAPER Urban groundwater quality in sub-Saharan Africa: current status and implications for water security and public health D. J. Lapworth 1 & D. C. W. Nkhuwa 2 & J. Okotto-Okotto 3 & S. Pedley 4 & M. E. Stuart 1 & M. N. Tijani 5 & J. Wright 6 Received: 4 June 2016 / Accepted: 6 December 2016 / Published online: 18 January 2017 # British Geological Survey, NERC 2017. This article is published with open access at Springerlink.com Abstract Groundwater resources are important sources of drinking water in Africa, and they are hugely important in sustaining urban livelihoods and supporting a diverse range of commercial and agricultural activities. Groundwater has an important role in improving health in sub-Saharan Africa (SSA). An estimated 250 million people (40% of the total) live in urban centres across SSA. SSA has experienced a rapid expansion in urban populations since the 1950s, with increased population densities as well as expanding geographical coverage. Estimates suggest that the urban population in SSA will double between 2000 and 2030. The quality status of shallow urban groundwater resources is often very poor due to Published in the special issue BHydrogeology and Human Health^ Electronic supplementary material The online version of this article (doi:10.1007/s10040-016-1516-6) contains supplementary material, which is available to authorized users. * D. J. Lapworth 1 British Geological Survey, Maclean Building, Wallingford OX10 8BB, UK 2 University of Zambia, Great East Road Campus, P.O. Box 32379, Lusaka, Zambia 3 Victoria Institute for Research on Environment and Development (VIRED) International, Rabuour Environment and Development Centre, Kisumu-Nairobi Road, P.O. Box 6423-40103, Kisumu, Kenya 4 Robens Centre for Public and Environmental Health, University of Surrey, Guildford GU2 7XH, UK 5 Department of Geology, University of Ibadan, Ibadan, Oyo State, Nigeria 6 Geography and Environment, University of Southampton, Highfield, Southampton SO17 1BJ, UK inadequate waste management and source protection, and poses a significant health risk to users, while deeper borehole sources often provide an important source of good quality drinking water. Given the growth in future demand from this finite resource, as well as potential changes in future climate in this region, a detailed understanding of both water quantity and quality is required to use this resource sustainably. This paper provides a comprehensive assessment of the water quality status, both microbial and chemical, of urban groundwater in SSA across a range of hydrogeological terrains and different groundwater point types. Lower storage basement terrains, which underlie a significant proportion of urban centres in SSA, are particularly vulnerable to contamination. The relationship between mean nitrate concentration and intrinsic aquifer pollution risk is assessed for urban centres across SSA. Current knowledge gaps are identified and future research needs highlighted. Keywords Groundwater quality . Sub-Saharan Africa . Urban groundwater . Nitrate . Microbiological contamination . Health Introduction Groundwater is the largest and most important water resource in Africa (MacDonald et al. 2012). It is often more reliable, in closer proximity to users, less vulnerable to pollution, and more resilient to climate variability than surface water (MacDonald et al. 2011; Lapworth et al. 2013). Access to safe and reliable water is critical for improving health and livelihoods for low-income communities in Africa and elsewhere globally (Hunter et al. 2010). Many expanding urban areas in sub-Saharan Africa (SSA) are dependent on groundwater for at least some, and many cases the majority, of domestic water 1094 supply (Adelana et al. 2008; Foster et al. 1999). Over the last three decades there has been a concerted effort to develop improved water supply and sanitation across Africa (Bartram and Cairncross 2010), a recent example being the UN Millennium Development Goals which had the target of halving by 2015 the population without sustainable access to improved sanitation (JMP 2008). Groundwater is considered the centrepiece of improved drinking-water provision in many parts of Africa (Foster et al. 2006). Within urban and periurban contexts, this has led to widespread development of groundwater resources beneath and in close proximity to urban centres across SSA. In addition, urban sanitation provision and waste management systems across SSA are inadequate, with an estimated average of 40% coverage for improved sanitation facilities (World Bank 2012). Water treatment options are often very limited and in many cases municipal facilities for waste and water treatment are overloaded or experiencing reduced functionality partly due to limited funding and poor governance. The high population densities found in urban areas has led to the proliferation of unimproved sanitation provision largely through the use of pit latrines, which are often little more than a hole in the ground, and are in very close proximity to wells and springs that are important for domestic use (Stenström 1996). Across large parts of SSA there is continued and accelerated expansion of urban and peri-urban settlements. A recent study (UNPF 2007) estimates that between 2000 and 2030 Africa’s urban population, compared to rural population, will double and become the majority. Overall, 37% of Africa’s population are currently urbanised and the urban proportion is growing (World Bank 2016a, b). While groundwater is considered the most resilient source of drinking water across much of Africa, the lack of adequate management of household and industrial waste in many expanding urban centres is a growing concern (Wang et al. 2012). This poor waste management practice has led to the groundwater resources below many urban and peri-urban areas being put under considerable pressure from pollution loading with clear implications for groundwater quality and public health. This is compounded when current and future climate extremes and increased urbanisation are also considered, which may lead to increased flood risks and related disease outbreaks (McMichael et al. 2006; Howard et al. 2016). Per-capita usage is also predicted to rise in line with prosperity which will put additional stress on available groundwater resources, many of which are found on low yielding basement aquifers (MacDonald et al. 2012). Future trajectories of growth of urban centres in SSA, notable for regions in West and East Africa, and increased demands on groundwater resources mean that urban centres are likely to be more dependent on groundwater in the future (UNEP 2008). Together, these factors challenge the security of groundwater resources in many urban areas across SSA. Hydrogeol J (2017) 25:1093–1116 Groundwater is the critical resource for human survival and economic development in extensive dr (...truncated)