|(a) Any irrigation system that is connected to a public or private potable water supply must be connected through a commission-approved backflow prevention method. The backflow prevention device must be approved by the American Society of Sanitary Engineers; or the Foundation for Cross-Connection Control and Hydraulic Research, University of Southern California; or the Uniform Plumbing Code; or any other laboratory that has equivalent capabilities for both the laboratory and field evaluation of backflow prevention assemblies. The backflow prevention device must be installed in accordance with the laboratory approval standards or if the approval does not include specific installation information, the manufacturer's current published recommendations. (b) If conditions that present a health hazard exist, one of the following methods must be used to prevent backflow; (1) An air gap may be used if: (A) there is an unobstructed physical separation; and (B) the distance from the lowest point of the water supply outlet to the flood rim of the fixture or assembly into which the outlet discharges is at least one inch or twice the diameter of the water supply outlet, whichever is greater. (2) Reduced pressure principle backflow prevention assemblies may be used if: (A) the device is installed at a minimum of 12 inches above ground in a location that will ensure that the assembly will not be submerged; and (B) drainage is provided for any water that may be discharged through the assembly relief valve. (3) Pressure vacuum breakers may be used if: (A) no back-pressure condition will occur; and (B) the device is installed at a minimum of 12 inches above any downstream piping and the highest downstream opening. Pop-up sprinklers are measured from the retracted position from the top of the sprinkler. (4) Atmospheric vacuum breakers may be used if: (A) no back-pressure will be present; (B) there are no shutoff valves downstream from the atmospheric vacuum breaker; (C) the device is installed at a minimum of six inches above any downstream piping and the highest downstream opening. Pop-up sprinklers are measured from the retracted position from the top of the sprinkler; (D) there is no continuous pressure on the supply side of the atmospheric vacuum breaker for more than 12 hours in any 24-hour period; and (E) a separate atmospheric vacuum breaker is installed on the discharge side of each irrigation control valve, between the valve and all the emission devices that the valve controls. (c) Backflow prevention devices used in applications designated as health hazards must be tested upon installation and annually thereafter. (d) If there are no conditions that present a health hazard double check valve backflow prevention assemblies may be used to prevent backflow if the device is tested upon installation and: (1) a local regulatory authority does not prohibit the use of a double check valve; (2) backpressure caused by an elevation of pressure in the discharge piping by pump or elevation of piping above the supply pressure which could cause a reversal of the normal flow of water or back-siphonage conditions caused by a reduced or negative pressure in the irrigation system exist; and (3) test cocks are used for testing only. (e) If a double check valve is installed below ground: (1) test cocks must be plugged, except when the double check valve is being tested; (2) test cock plugs must be threaded, water-tight, and made of non-ferrous material; (3) a y-type strainer is installed on the inlet side of the double check valve; (4) there must be a clearance between any fill material and the bottom of the double check valve to allow space for testing and repair; and (5) there must be space on the side of the double check valve to test and repair the double check valve.