How to Repair a Leaking Water Supply Line

Water supply leaks are deceptive problems. A small drip from under the sink or along a basement copper run might seem minor until you realize it's been soaking into your framing for weeks. The good news is that most supply line leaks are fixable without calling a plumber, and the repair itself takes an hour or two. The key is identifying whether you're dealing with a loose connection, a degraded fitting, or actual pipe damage—and then matching the right fix to the problem. Done well, a repaired supply line holds pressure cleanly and leaves no trace of the leak.

1. Shut Off and Locate. Turn off the main shutoff valve at your water meter or where the supply enters the house. Open a faucet to relieve pressure in the lines, then dry the leaking area thoroughly with towels. Identify whether water is coming from a connection point (fitting, valve, or coupling) or from the pipe itself. Mark the leak location clearly with tape.
2. Tighten First, Test Fast. Place an adjustable wrench on the connection nut closest to the leak. Hold the fitting body steady with a second wrench to prevent twisting the pipe, then turn the nut clockwise a quarter to half turn. Do not over-tighten; you're looking for snug resistance, not force. Turn the water back on and check for leaks.
3. Swap the Ferrule. Shut off the water again and open a faucet. Using two wrenches, disconnect the leaking fitting by holding the fitting body and turning the nut counterclockwise. Slide the old ferrule (the small brass or plastic ring) and compression sleeve off the pipe end. Slide a new ferrule onto the pipe, then thread the nut back on hand-tight. Use wrenches to snug it firmly—again, hold the fitting body steady. Restore water pressure and test.
4. Cut and Couple Pipe. If the leak is coming from the pipe body itself (not a connection), shut off water and relieve pressure. Use a hacksaw or tubing cutter to remove the damaged section, cutting clean, perpendicular lines. Slide coupling nuts and ferrules onto each cut end, then insert a new length of pipe (copper, PEX, or matching material) between them. Tighten the nuts firmly using two wrenches, then turn the water back on and monitor for leaks.
5. Solder for Permanence. This method works only on copper supply lines and requires a propane torch, solder, and flux. After shutting off water and cutting out the damaged section, deburr the pipe ends with sandpaper. Apply flux to both the pipe end and the inside of a new coupling, heat the joint with the torch until the copper begins to glow slightly, then feed solder into the joint—it will flow into the heat. Let cool for 5 minutes before handling. This creates a permanent joint stronger than compression fittings.
6. Monitor and Dry. Turn the main water supply back on slowly, opening a low faucet first to avoid air-hammer shock. Leave the repair site exposed for at least an hour while you monitor it closely. Check under sinks, in the basement, and at all connections for any weeping or dripping. Dry out any water that leaked before the repair using towels and fans to prevent mold growth.
7. Stop It from Happening Again. Inspect the area around the repair for conditions that caused the leak. Check for excessive vibration from water hammer (install a shock arrestor if lines bang when you turn off faucets), corrosion on copper pipes, or freeze damage. If the supply line is in an uninsulated exterior wall or attic, wrap it with pipe insulation. If corrosion is widespread along the pipe run, plan for professional replacement of that section.
8. Document and Track. Take a photo of the repair location and the date you completed it. Add a note to your home maintenance log. Check the area monthly for the first several months, especially after the water heater cycles or during seasonal pressure changes. Most successfully repaired connections remain leak-free indefinitely, but early vigilance catches any failures before they cause damage.