Water management activities involve a complex and interconnected web of science, infrastructure considerations, societal expectations, and institutional limitations that has evolved over time. Much of the water management system's current complexity developed in response to the interests of local water users and land owners, historical water supply and demand issues, political demands, and water quality and environmental considerations. Climate change poses a new set of questions for water managers and may require more flexible solutions than those that have evolved historically. Although the implications of changes in the climate on water supply and demand are recognized (if not well quantified), ongoing changes in temperature and precipitation, as well as the linkages between environmental and societal factors, lead to major uncertainties in future conditions. New tools, techniques, and institutions will be needed to sustain water supplies for communities and watersheds in the future.