This study explores water scarcity as a threat to US national security. The region in question is the "arc of instability" extending from North Africa to China. Given the wide array of US interests in this region, the study specifically addresses the question; "Does US national strategy provide the most advantageous approach to protect national security interests in an increasingly water-scarce world?" Three major conclusions surfaced. First, water scarcity is an emerging problem that is destabilizing and threatens US interests. Second, current water policy is bared solely on a moral imperative to help the needy but stops well short of addressing water scarcity as a security threat either now or in the future. Third, advancing and protecting US interests will become more difficult as scarcity becomes more acute in the first quarter of this century. The study begins with a primer on water availability and its destabilizing nature. Next, four root causes of scarcity are classified and then related to US national interests. The assessment that US strategy does not address scarcity results from an examination of primary sources of current US strategy. Finally, critical elements pertinent to a security strategy that addresses the threat of water are offered along with areas for further study.