RIPARWIN (Raising Irrigation Productivity and Releasing Water for Intersectoral Needs) is a four-year action-research project located in Tanzania, funded by the UK's Department for International Development (DFID). It is a study of river basin management in an environment typical of bi-seasonal sub-Saharan Africa where formal governance structures are relatively underdeveloped and where the challenge is to supply and allocate water between farmers, rural poor people, the environment and for electricity generation. The project is examining the commonly-held theory that if irrigation efficiency and productivity can be raised, this 'frees up' water to other farmers and sectors. The project is also testing the normative views that water should flow to the sector representing the highest economic benefit rather than protecting poor livelihoods in the interior of Tanzania. The project is implemented by 3 organisations; the Soil Water Management Research Group (SWMRG), the International Water Management Institute (IWMI) and the Overseas Development Group (ODG). The contract is between ODG and Knowledge and Research (KAR) of DFID. The project is studying the upper part of the Great Ruaha River, from the Usangu Basin to the exit of the Mtera/Kidatu power-generating complex. We believe that the research has been successful in testing new ideas, creating sub-catchment user groups, assembling decision-aid tools that were developed with stakeholders' participation, exploring more appropriate ways of generating informal and formal water rights, and testing the prevailing questionable theories about the inefficiency of irrigation and of the principles behind allocation imperatives. Our intention is to ensure these ideas are built a more appropriate and supportive policy framework towards integrated basin management. The case study indicates that the efficacy of river basin management might best be judged by an ability to attend to local and micro-scale issues that are normally below the 'radar' when compared to perceived macro inequities in supply.