This paper reports an approach to introduction of new water management in irrigation development project based on the farmers' water use custom of rice cultivation in paddy fields in Cambodia. Field surveys on farmers' water use customs for rice farming was conducted, and following features were found; 1)Farmers have no organization for water management, 2)They may take water in canals into their paddy fields freely, 3)They share the water in their paddy fields using the network of plot to plot irrigation, 4)The sprit of reciprocity is the basis of their water sharing. Some activities in water users' workshop aimed to adapt their customs of water use to new irrigation facilities; water route mapping, discussion on water use problems and collective work for canal maintenance.
