Increasing competition for resources across the globe reveals the finite nature of the resources that fuel our societies. The study of peak resource consumption originated with the concept of “peak oil,” the idea that oil production will reach an upper limit and then decline. Applied to water resources, the concept of “peak water” illustrates the tension between the human need for water and the ecological limits of using that water. Understanding the links between human demands for water and peak water constraints can help water managers and planners move towards more sustainable water management and use.