The science on which solutions to present and future global water problems must be based does not fall within the purview of a single discipline but rather is truly multidisciplinary and inherently interdisciplinary. It embodies the fundamental physical and biological sciences as well as applications of those sciences and substantial contributions from the engineering sciences, hydrology, climatology, and geology. A host of institutional, policy, and management issues must be addressed by fundamental and applied social sciences, which have been largely neglected in recent decades.