The growth in the number of human beings on Earth is undeniably a challenge for the planet, especially in terms of nonrenewable resources. However, scientific knowledge of the issues linking population and water should not be limited to only two variables – quantity of water and number of human beings. Other phenomena at play must be taken into account, and in particular at a micro-scale level. One of the central issues is certainly that of inequity in access to and the use of water, and its consequences. Population health, social and economic inequalities and their measures (including the questions of gender and poverty), governance of the hydro-socio-system, and in particular the participation of all stakeholders, are among the research priorities in the field of population, development, and the environment. This review’s first section summarizes international-scale dialogues on the population water issue. It is followed by a review of some empirical research demonstrating the associations between population health and water. Finally, we present some illustrations of the complex interrelations between water resources and socio-demographic characteristics of populations. The chapter concludes on the need for a mixed and interdisciplinary approach, a dialogue between the social sciences, biomedical sciences, and the life and earth sciences.