A plumbing system must be installed to preclude backflow of a solid, liquid, or gas contaminant into the water supply system at each point of use at the food establishment, including on a hose bibb if a hose is attached or on a hose bibb if a hose is not attached and backflow prevention is required by law, by:

(1) Providing an air gap as specified under WAC 246-215-05215; or

(2) Installing an approved backflow prevention device as specified under WAC 246-215-05220.