In sub-Saharan Africa 85% of those without access to safe water live in rural areas where the consequent poverty and ill health disproportionately affect women and children. The widespread development of groundwater is the most affordable and sustainable way of improving access to secure water for the rural poor on the scale required to achieve current coverage targets. However, groundwater resources vary considerably across the continent, and the sustainable development of the resource depends on an accurate understanding of the hydrogeology. To develop secure water supplies, the quantity, quality and sustainability of groundwater resources must be known to ensure that key decisions are informed by knowledge of resource conditions. Communities must also be involved at every stage of the process and given the authority to manage and maintain sources. There is a danger that the current pressure to achieve ambitious coverage targets will result in short cuts being taken and, although many new sources are constructed, they will not be secure.