Nonpoint source pollution from agriculture represents a major threat to the quality of water in the European Union (EU) context. As part of the implementation process of the EU Water Framework Directive, voluntary cooperation between water suppliers and agricultural stakeholders has been recently promoted for limiting diffuse pollution from agriculture at the water catchment level in France. Based on a conceptual framework combining transaction cost economics and the social-ecological system (SES) framework, this paper identifies the conditions under which such collective action is effective for the restoration/maintenance of water quality. This analysis relies on a cross-case comparison of cooperation in six drinking water catchments based on primary data collection at the national, water basin and local levels. Variables related to the hydrogeological system, the stakeholders involved, the contracts governing cooperation and the economic and policy contexts are shown to interact as they influence collective action. The results highlight the importance of the adaptation of contract incentives to the characteristics of the local context and the potential complementarities between informational, regulatory and economic policy tools for enhancing the effectiveness of collective action for water pollution control.