NGA 71: Operator Excavating and Backfilling in the Vicinity of a Pipeline (Critical AOC) Practice Test

Color marks for underground utilities follow a standardized scheme so crews can quickly identify what’s below the surface. Purple is used to indicate non-potable water lines, including reclaimed water and related non-potable systems like slurry lines in some practical contexts. That distinction is important because it signals that the fluid isn’t safe for drinking and must be treated differently in planning, testing, or connection work. Other colors are reserved for other utilities—blue for potable water, green for sewer, red for electric, yellow for gas, etc.—so purple stands out as the marker for non-potable slurry lines. Always verify local codes and facility owner guidance, but purple is the color commonly associated with non-potable or reclaimed water systems.