Further steps need to be taken to halt excessive groundwater abstractions, including through improved monitoring and the introduction of charges on abstractions from overexploited aquifers. Its climate and the physical characteristics of its environment, such as the prominence of mountain ranges close to the coasts or soil characteristics, make natural water endowments highly unequally distributed across space and time. These characteristics have determined water policies, which used to aim at increasing supply by constructing large dams with government support. With over 1 300 dams, Spain is estimated to be the country with the 4th largest number of dams in the world (after the United States, India and China, Martinez-Cortina, 2010). Over the past century this policy increased water abstractions per inhabitant to a higher level, on average, relative to renewable resources, than in most other OECD countries (Figure 4.1), relatively low population density notwithstanding.