The search for fresh water—to drink, to bathe in, to irrigate crops—is a problem as old as civilization. Across the ages, cities have thrived where the supply is abundant and collapsed in the face of drought. Remarkably, despite the technological progress characterizing the modern era and the fact that most of Earth's surface is covered by oceans, the availability of fresh water remains a pressing concern throughout the world. In this special section, we highlight some of the diverse contemporary scientific and engineering projects dedicated to obtaining and maintaining freshwater resources.

We begin with a Review by Oki and Kanae (p. 1068) on current understanding of the natural water cycle, and in particular the role of climate change in determining freshwater abundance. A related Review in this week's issue by Peterson et al. (p. 1061) focuses more specifically on the Arctic region. Even in regions of abundant fresh water, contamination and disease can disable local communities. Schwarzenbach et al. (p. 1072) present a Review of chemical contamination problems. They note that although effective strategies have been implemented to remediate large-scale pollutants, a substantial amount of work looms ahead to cope with the numerous different compounds that are present at lower concentrations. In particular, collaborative efforts among chemists, geologists, and toxicologists are increasingly important to characterize the complex interactions of these compounds in the environment. Fenwick's Perspective (p. 1077) follows with an optimistic view of the ongoing effort to combat waterborne diseases accompanying development programs in Africa, highlighting the role of drug donations from the pharmaceutical industry.

It may seem strange to many people that modern societies cannot fulfill their water needs simply by purifying ocean water. Tal offers a Perspective (p. 1081) about the multipronged strategy—of which desalination is an increasing component—that Israel has adopted to procure fresh water in an arid environment. Bohannon highlights the resource issues specific to the Gaza region in an accompanying News story (p. 1085). Another News story by Service (p. 1088) focuses more broadly on current developments in desalination technology. Additionally, two related stories by Stone and Jia (p. 1034) and Bagla (p. 1036) in the magazine's News Focus section describe large-scale engineering efforts in China and India to supply fresh water across extensive geographical areas.

Inevitably, water resource management is a political problem as well as a scientific one (see the related Editorial by Kennedy and Hans on on p. 1019). It is clear that ensuring adequate supply will necessitate continuing collaborations across a great range of disciplines. The approaches described here offer a measure of hope for the future.

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