This report addresses multilevel governance challenges in water policy implementation and identifies good practices for coordinating water policy across ministries, between levels of government, and across local actors at subnational level. Based on a methodological framework, it assesses the main “coordination gaps” in terms of policymaking, financing, information, accountability, objectives and capacity building, and provides a platform of existing governance mechanisms to bridge them. Based on an extensive survey on water governance the report provides a comprehensive institutional mapping of roles and responsibilities in water policy-making at national/subnational level in 17 OECD countries. It concludes on preliminary multilevel governance guidelines for integrated water policy.