Unprotected well heads can be sources of nitrate and other pollutants in groundwater. This risk can amplify when other wells are operating in the area. The California State Water Resources Control Board compiled a list of well and water protection practices in its 2015 publication The Guide for Private Domestic Well Owners. The well head protection practices are applicable to agricultural and domestic wells. The Guide also presents additional information about domestic well use, well construction and destruction, and water quality protection, testing, and treatment. A fact sheet is available here.