Water distribution systems in Santa Clara County, Calif., may be damaged and rendered inoperable by a large earthquake or other disaster. In such an event, individual agencies may have to implement emergency measures to supply water for drinking, firefighting, decontamination, or other purposes. In Santa Clara County, 128 wells have been identified as potential water-supply sources in emergencies. The criteria used to select the wells are: yield of at least 3 liters per second (50 gallons per minute), good water quality, ready accessibility, and available emergency power. Purification methods of small water supplies are described. (Woodard-USGS)