Abstract
Over-use or mismanagement of water can occur when institutions fail to meet various users' demand. This study evaluate the extent to which water management institutions are effective and legitimate in governing water allocation and distribution in Farmer-Managed Irrigation Schemes in Iringa rural and Kilombero Districts, Tanzania. Institutional performance was evaluated using Ostrom's eight design principles or indicators. Findings indicate that there is significant associations between scheme type (traditional and semi-improved irrigation) and clearly defined boundaries of resource and of appropriators; participation in decision making; collective action and conflict resolution mechanisms. Clearly defined boundaries of resource and users rights', congruence between appropriation and provision rules and local conditions and fair representation in water decision making bodies principles seemed to perform better in the semi-improved irrigation schemes. The traditional schemes seem to have a better grip on monitoring, legitimate sanctions, collective actions and conflict resolution mechanisms that are swift and low-cost efficient. Limited (39%) involvement of farmers in water decisions created a sense of dispossession leading to negative attitudes towards a new water management institution. This study underscores the importance of local water users’ participations in water management decision bodies in order to come up with effective, cost efficient and legitimate formal institutions. Formalization of any water management institutional interventions by policy makers should build on the existing informally established regulations and take into account local conditions.