D.C. Mun. Regs. tit. 25, r. 25-C6421
No direct mechanical connection shall be made between the potable water supply and the swimming pool or spa, chlorinating equipment, or the system of piping for the swimming pool or spa, unless it is protected against backflow and back-siphonage in a manner approved by the Department of Consumer and Regulatory Affairs, or through an air gap meeting the approval of the Department of Consumer and Regulatory Affairs.
Where it is not practicable to provide the minimum air gap, the connection to the fixture, equipment or appliance shall be equipped with a backflow preventer assembly of a type and at a location approved by the Department of Consumer and Regulatory Affairs.
Backwash water or drainage waters of a swimming pool or spa shall be discharged into a sanitary sewer through an approved air gap, or by other means approved by the Department of Consumer and Regulatory Affairs.
Deck drainage shall be discharged through an indirect drain.
D.C. Mun. Regs. tit. 25, r. 25-C6421