D.C. Mun. Regs. tit. 25, r. 25-C402
The pool water shall be 0.5 or less NTU and the main drain grate shall be readily visible from the pool deck.
The water in an aquatic facility shall be sufficiently clear such that the bottom is visible while the water is static at all times the aquatic facility is open or available for use.
Depth markers shall be not less than four inches (4 in.) (one hundred and two millimeters (102 mm)) in height. The color of the numbers shall contrast with the background on which they are applied and the color shall be of a permanent nature. The lettering shall spell out the words "feet" and "inches" or abbreviate them as "Ft." and "In." respectively. Where displayed in meters in addition to feet and inches, the word meter shall be spelled out or abbreviated as "M".
Swimming pools built after adoption of these regulations, shall add a four inch by four inch square (4 in. x 4 in.) (10.2 cm x 10.2 cm) marker tile in a contrasting color to the swimming pool floor, and/or shall add a main suction cover outlined in a contrasting color to the swimming pool floor which are located at the deepest part of the swimming pool floor.
Swimming pools over ten feet (10 ft.) (3.0 m) deep, an eight inch by eight inch square (8 in. x 8 in.) (20.3 cm x 20.3 cm) marker tile in a contrasting color to the swimming pool floor or main suction outlet shall be located at the deepest part of the swimming pool.
Spa pools and swimming pools with heaters shall have a maximum water temperature of one hundred and four degrees Fahrenheit (104° F) (forty degrees Celsius (40° C)).
D.C. Mun. Regs. tit. 25, r. 25-C402