Fresh water is a fundamental resource, integral to all ecological and societal activities, including food and energy production, transportation, waste disposal, industrial development, and human health. Yet fresh water resources are unevenly and irregularly distributed, and some regions of the world are extremely water-short. As we approach the twenty-first century, water and water-supply systems are increasingly likely to be both objectives of military action and instruments of war as human populations grow,  as improving standards of living increase the demand for fresh water, as global climactic changes make water supply and demand more problematic and uncertain. This article outlines the links between water and conflict, and presents some of the issues and information that make it possible to assess when and where water-related conflicts are most likely to occur. Tools for reducing the risks of such conflicts are also presented, together with recommendations for policymakers.