This paper argues for a coordinated effort to provide improved water resources information by water scientists both within the region and from outside. It further proposes a unified approach based on hydrological modelling that incorporates realistic measures of uncertainty and that can be applied to the region as a whole using a common methodology. The concept is designed to make the best use of all available data sets, including local observations as well as emerging global data. The suggested approach has scientific credibility (based on previous studies), is technically feasible and offers a range of long-term benefits. The overall conclusion is that without a project of this type, water resources planning and management decisions in the region will continue to be based on inadequate information and unquantified uncertainties. Keywords: Sub-Saharan Africa, Water resources assessments, Hydrological modelling, Uncertainty.