Social capital is one of the major drivers in the diffusion process of water system innovations within agrarian communities in a watershed. However, there is limited information on the nature and extent of social capital, and how it influences the diffusion of water system innovations at community level. This paper explores the role of social capital on the uptake of water system innovations in the Makanya watershed. Information on role of social capital in the diffusion of water systems innovations was analysed using data collected through key informants interviews, focus group discussions and structured questionnaire. Qualitative and quantitative methods were used to analyse the data and the results were summarized in tables and figures. Results show that the social capital elements, which are key to adoption of WSIs are group belonging and information pathways. Group belonging was significant in the diffusion of terraces at P < 0.001 in the upland and P < 0.1 at watershed level. Information and communication pathways were not significant in the diffusion of terraces but were significant (P < 0.01) in the diffusion of ndivas and diversion canals. This paper recommends the inclusion of these parameters in the design of uptake and up-scaling strategy for WSIs especially in the study area.