Which distance is the horizontally required minimum from a potable water supply line for sewer lines when possible?

• A. 9 ft horizontally and 3 ft vertically above
• B. 10 ft horizontally and 2 ft vertically above
• C. 8 ft horizontally and 2 ft vertically above
• D. 9 ft horizontally and 2 ft vertically above

Answer: (D)

To prevent cross-contamination between sewer and potable water lines, you want a solid separation both horizontally and vertically. The minimum horizontal separation, when possible, is nine feet. In addition, the potable water line should sit at least two feet higher in elevation than the sewer line, which helps keep any potential leakage away from the water supply.

So, the best choice is nine feet of horizontal distance with a two-foot vertical separation where the water line is above the sewer line. The other options either shorten the horizontal buffer or change the vertical offset beyond what’s required, and thus don’t meet the stated minimums.