Taking a closer look at the interplay between the different public actors involved in water policy making, the chapter proposes a tentative taxonomy of the main governance challenges, based on selected indicators and data collection from the OECD survey on water governance. Detailed horizontal and vertical co-ordination challenges for 17 OECD countries are synthesised in the country profiles attached to this report. Taking stock of existing principles, guidelines, indicators, indexes and checklists for good governance in the water sector, this chapter presents a “reading template” identifying seven common multi-level governance “gaps” and attempts to assess, based on selected proxies, their importance in several OECD countries.