Water is a vital renewable resource that is increasingly stressed by multiple and competing demands from people, industry, and agriculture. When water becomes unavailable or unusable, life itself cannot be sustained. Changes in supply and demand for water are driven by population growth, climate change, and our energy and land use choices. Poverty frequently precludes the ability of many people to respond and adapt to water insecurity. In this essay, we discuss the effects of these drivers on the diminution of rivers, aquifers, glaciers, and the severe pollution that renders some water resources unusable. While technologies for water reuse, desalination, aquifer replenishment, and better water pricing are important solutions, the recognition of water as a profoundly threatened resource and as a basic human right is essential for providing sustainable water for future generations.