Journeyman Plumber ExamWater Supply SystemsMedium
A plumber is installing a water service line from the public water main to a new single-family residence. The local plumbing code specifies that the water service line must be installed with a minimum depth of cover to protect against freezing. In a region with a typical frost line of 30 inches, what is the most common minimum burial depth for a water service line, assuming no other specific local requirements are more stringent?
- A48 inches
- B24 inches
- C12 inches
- D36 inches
Show answer & explanationAnswer & explanation
Correct answer: D. 36 inches
To protect against freezing, water service lines must be installed below the local frost line. A common plumbing code practice is to require a minimum of 6 inches below the frost line, or at least 36 inches total depth, whichever is greater, in regions with a 30-inch frost line.
Why the other options are wrong
- A. 48 inches would also protect, but 36 inches is the most common *minimum* depth for this frost line scenario.
- B. 24 inches is still above the 30-inch frost line, making it vulnerable to freezing.
- C. 12 inches is typically insufficient to protect against a 30-inch frost line.
Water Service Line Burial Depth
The minimum vertical distance from the finished grade to the top of a water service pipe, primarily to protect against freezing and physical damage.
- Must be below the frost line
- Commonly 6-12 inches below frost line
- Varies by local code and climate
Memory trick: Below the frost, pipes are never lost!