Harnessing natural attenuation of pharmaceuticals and hormones in rivers.

W ater scarcity has become a harsh reality in many parts of the world. In the past, water needs were often met by building large dams and importing water over long distances. This approach is proving increasingly infeasible because social and environmental costs are too high (1). As the increased need for dependable water resources mirrors the growth in population, many communities are turning to reclaimed water to meet their demands. A guiding vision for managing water supplies is to “close the water loop”: Consumers from large cities to individual households use and repeatedly reuse their local water resources, drastically reducing the need to import water. Currently, nonpotable reuse is the most common form of water reclamation. For example, Table 1 summarizes the volumes of water treated for reuse in California in 2002. Pressure to reuse water is increasing, and natural processes may be an easy and cheap approach to removing many contaminants of concern.