In an effort to take stock of existing initiatives, the “OECD inventory: Water governance indicators and measurement frameworks”, launched on line in October 2015, mapped 78 instruments (e.g. indicators, maps, databases and assessment tools, see Table 2.2) for measuring and evaluating several water governance aspects. Most of these indicators relate to specific functions (water, sanitation and hygiene and integrated water resources management), scales (e.g. national, basin) or governance dimensions (transparency, capacity, etc.), The most relevant toolkits and indicators for the implementation of the OECD Principles on Water Governance are summarised in Table 2.1. The challenges are related to the complexity of the water governance dimensions to be assessed, data availability, data collection through expert views, comparability over space and time, and the difficulty in drawing causality linkages between outcomes measured by indicators and policies aiming at generating certain impacts (Figure 2.2). It contains evidence-based tools and advice as well as country examples showcasing practices which have been successfully tested in a number of countries.