CONTEXTThe ancient Sri Lankan village tank cascade system (VTCS) is a unique agricultural system that irrigates 35% of rice lands in Sri Lanka. Climate change, population growth, and social determinants are increasing pressure on VTCS, and the available water resources are being limited and competing with other water users. Therefore, effective water management on the field and landscape scale needs attention to address these challenges. OBJECTIVESince community-based water management bodies have been recognized as a leading approach for effective field-level water management, this study aimed to assess the behavior of farmer organizations (FOs), understand their capacities for field-level water management, and determine improvements required to achieve more effective field-level water management. METHODSWe surveyed 357 respondents from 21 FOs in the Deduru Oya river basin. FO behavior in five categories was assessed: 1) organizational rules, legitimacy, and culture; 2) organizational hierarchy and decision-making; 3) leadership; 4) communication and coordination; and 5) motivational incentives and organizational stability. Respondents rated their perception of the organizational behavior of the FO they participate in on a Likert scale. In addition, we conducted key informant interviews with 11 field officers of relevant government bodies who work closely with the FOs we studied. RESULTS AND CONCLUSIONFOs showed great diversity in their organizational behavior. Overall transparency, participatory decision-making, internal communication, and leadership were identified as key behaviors supporting efficient water management by FOs. Organizational culture, external communication, and organizational stability were all found to have significant improvement needs. FO behaviors in terms of organizational culture have major gaps in several areas, including poor organizational legitimacy awareness, poor financial accountability, unhealthy revenue generation, insufficient environmental consideration, and poor record keeping. Interestingly, FO members from different hierarchical layers disagreed on behavior within their own FOs. Additionally, conflicting responses among FOs and government agency field officers were also observed, highlighting the need to inspect field officers' actions by senior authorities. There is a need to improve FO behaviors in identified weak areas for better irrigation water management. SIGNIFICANCEThe recommendations of this study offer multi-scale solutions, including solid capacity building through knowledge sharing and highlighting the gaps aimed at strengthening FO behaviors that support effective field-level water management. The findings and recommendations are informative in terms of investments required to enable FOs to fulfill their potential as efficient water managers at the community scale. Furthermore, these findings may help in national policy making.