Trap seal depth (general) is between which measurements?

• A. 2-4 inches
• B. 4-6 inches
• C. 6-8 inches
• D. 1-2 inches

Answer: (A)

Trap seal depth is the vertical depth of water held in a trap to form a barrier that blocks sewer gases. In general practice, that water seal is about 2 to 4 inches deep. This range keeps the seal strong enough to prevent odors from escaping while still allowing the trap to drain and vent properly. If the depth drops below about 2 inches, the barrier becomes unreliable and odors can get through. If it were much deeper—approaching 4 inches or more—it can complicate venting or siphoning in some setups, though the exact limits can vary by code. So, the standard general range is 2-4 inches.