Factors affecting the success of rural water supply programmes are investigated in this work. Data is gathered from three evidence sources: a case study of four South American nations, interviews with experienced personnel and the literature. These are combined in an iterative hypothesis building procedure which integrates evidence from all sources. Eight factors are identified along with supporting evidence for each – these are divided into factors relating to national water sector structure and those relating to water supply programmes. The inter-factor dependencies lead to a discussion of the implementation potential for each factor. Implementation of the factors in future water supply programmes is expected to lead to more successful outcomes. The procedure in this work could be extended to analyze related disciplines such as urban water supply or sanitation.