The model rules provide the criteria for assuring that an adequate supply of safe drinking water and adequate safe sewer facilities are available to residential areas in accordance with state standards established by the Texas Department of Health and the Texas Commission on Environmental Quality. The model rules prohibit the establishment of residential developments with lots of five acres or less without adequate water supply and sewer services, prohibit more than one single-family, detached dwelling to be located on each subdivision lot, and establish minimum setbacks to ensure proper operation of water supply and sewer services and to reduce the risk of fire hazards.