Population growth and competing demands within natural watershed boundaries may make existing drinking water supply inadequate for future demand. Watershed management or source control is the most cost-effective method for protecting our drinking water resources and aquatic systems; meeting our long-term water quality goals; and reducing expensive treatment, especially for waterborne pathogens. The California Department of Health Services’ (DHS) Surface Water Treatment Regulation required domestic water suppliers using surface water sources to conduct a sanitary survey of their water supply watersheds by January 1, 1996, and to update that survey every 5 years thereafter. The sanitary survey is a tool of source control. This discussion of watershed management programs and sanitary survey technologies used in California is intended to provide Taiwan and other Pacific Rim countries with the benefit of California experience in this area. It will also assist Taiwan and other Pacific Rim countries in preserving, improving, and protecting drinking water and natural water qualities.