Know Your System
Supply Lines and Drain Lines Are Two Different Systems
People say “water line” and “sewer line” in the same breath, but they’re opposite systems with opposite jobs — confusing them leads to the wrong service call.
Water supply lines — this page — bring clean, pressurized water into the building: from the city main, through the meter, along your private line, and through the pipes in your walls to every faucet. Problems show up as leaks, pressure loss, discolored water, or an unexplained spike in the water bill.
Drain and sewer lines carry wastewater out by gravity. Problems there show up as slow drains, gurgling, and backups — and that calls for sewer line repair or drain cleaning, not this page.
The practical test is simple: water coming out where it shouldn’t (a leak, a wet spot, a hissing pipe) means supply-line territory; water that won’t go away where it should (a drain that won’t empty) means drainage territory. Describing it that way gets you to the right diagnosis faster.