Collaborative management has developed as a main approach to solving complex environmental problems such as diffuse water pollution from agriculture. This paper aims to understand the drivers of farmers’ participation in collaborative water quality management. The role of farm characteristics, farmers’ profiles and farmers’ social networks is more particularly investigated while taking into account transaction costs. The study relies on a statistical analysis of data collected in two drinking water catchments in France. The results show that larger, more profitable farms with more equipment and access to off-farm income are more likely to participate in collaborative processes for water quality management. Furthermore, farmers’ involvement in agricultural and nonagricultural networks has a strong positive influence on their participation. These results suggest that significant costs, including transaction costs, are associated with farmers’ participation in collaborative management. Targeted support for smaller, financially constrained farms and less-connected farmers could enhance the effectiveness of the collaborative approach to diffuse pollution control.