The OECD Principles on Water Governance, rather than providing a general toolkit unfit for most situations, deliver and widely diffuse recommendations to policy makers to consider when reviewing existing policies or defining new ones (Table 1.4). Moreover, rules are not necessarily embedded in laws: in many countries, they are rooted in customary water rights. However, there is an institutional layer (meso-institutions), which is often either neglected or even missing, and that links the macro-institutional layer at which rules are defined and the micro-institutional layer at which implementation takes place.