Water scarcity in the fast-growing megacity of Lagos, Nigeria and opportunities for managed aquifer recharge

In the last three decades, the world has experienced a rapid emergence of megacities. The increasing demographics, urbanization, and water demand brought severe and undesired effects on the quantity and quality of their water resources. A prime example is Lagos (Nigeria, West Africa), which is projected to become the world's largest city by 2100, and faces water scarcity challenges common to other megacities of developing countries. A literature review reveals the vast gap between water demand and regulated supply, inadequate knowledge and information on the current state of water (re)sources, and major, yet unregulated, use of groundwater. It further highlights the impacts of uncontrolled wastewater discharge into surface waters and aquifers, the role of increasing paved surfaces and blocked drainages on flooding, the inadequate supply of potable water, and the unsustainable abstraction of groundwater. Here, we examine the potential of managed aquifer recharge (MAR) to address these recurrent challenges across the megacity. The analysis reveals the opportunities and potential risks associated with the capture of wastewater, storm water, and brackish surface water for MAR. These waters, after appropriate treatment and subsurface storage may bridge the growing water supply-demand gap and mitigate the effects of groundwater (over)exploitation, including aquifer depletion, saltwater intrusion and land subsidence. Immediate efforts should focus on improving the conceptual and quantitative knowledge of Lagos' hydrogeology and groundwater resources through comprehensive spatial-temporal groundwater monitoring and socio-economic studies of groundwater access and use. The insights provided may inform other fast-growing coastal megacities in Africa and the wider developing world. This article is categorized under: Science of Water > Water and Environmental Change Engineering Water > Water, Health, and Sanitation Human Water > Value of Water Science of Water > Hydrological Processes