How to Fix a Leaking Shutoff Valve

Water underneath a sink often leads to immediate panic, but a weeping shutoff valve is rarely a catastrophe. Most modern supply valves use a simple compression seal that, over years of stagnant position, loses its elasticity and begins to weep at the handle stem. If you catch it early, you can usually stop the leak without cutting into the pipes or calling a professional. Done well, this repair stops the drip permanently and ensures your valve will operate smoothly the next time you need to kill the water to a fixture. The goal is to reseat the packing or replace the internal O-ring while ensuring the connection to the supply line remains undisturbed. Keep a bucket and a handful of rags nearby, as even a small valve holds enough water to surprise you.

  1. Make Room to Work. Remove all items from under the sink and place a small bucket or a folded towel directly beneath the valve. Clearing the area gives you the necessary room to maneuver your wrench without knocking into drain lines.
  2. Tighten the Seal First. Locate the hex-shaped packing nut sitting directly behind the valve handle. Use an adjustable wrench to turn it clockwise about an eighth of a turn, effectively tightening the internal seal.
  3. Watch for the Drip. Wipe the valve completely dry with a rag and monitor it for five minutes. If the moisture does not reappear, you have successfully compressed the seal and finished the job.
  4. Kill the Main Line. If the leak persists, you must turn off the main water supply to the house. Open the sink faucet fully to drain the remaining water pressure from the line before proceeding.
  5. Expose the Stem. Loosen the screw in the center of the valve handle and pull the handle off to expose the stem. Use your wrench to fully unscrew the packing nut and remove the stem assembly.
  6. Swap the Seal. Remove the old rubber washer or O-ring from the stem using a small screwdriver. Coat the new replacement part in a thin layer of heat-proof plumbing grease and seat it firmly into the groove.
  7. Reassemble and Verify. Reinstall the stem, tighten the packing nut until snug, and replace the handle. Slowly turn the main water supply back on and check for any signs of moisture around the valve stem.