The paper describes an assessment of a large spring-fed piped water supply scheme in Ethiopia. Constructed in the mid-1990s, the scheme has recently reported yield problems. These problems threaten the sustainability of the scheme and the success that it has achieved in supplying over 70,000 people. The assessment indicated possible reasons for this, both in terms of the natural resource and the management of the water system. The very limited data that were available with regard to the operation and functioning of the system made it difficult to draw clear conclusions and underlined the need for data collection processes to be designed into the operation and management of water supply projects.