How to Fix a Leaking Shutoff Valve Under the Sink

Shutoff valves are the unsung heroes of your plumbing system, sitting quietly under the sink until the day a faucet fails or a pipe bursts. When these valves start to leak—usually from the handle stem while in the open position—it is often a sign that the internal packing material has hardened or the compression nut has loosened over time. Ignoring a drip here can eventually ruin the vanity cabinet floor or lead to an annoying puddle inside your storage space. Fixing this is a straightforward task that requires nothing more than a steady hand and a pair of wrenches. Most leaks at the valve handle can be resolved in minutes without turning off the water to the entire house, provided you take your time and do not overtighten the hardware. Follow these steps to stop the moisture and restore the integrity of your under-sink plumbing.

  1. Clear the Work Zone. Remove all cleaning supplies and vanity items from under the sink. Place a small bowl or towel directly beneath the valve to catch any residual water.
  2. Tighten the Packing Nut. Locate the packing nut, which is the hexagonal nut sitting directly behind the valve handle. Use one wrench to hold the valve body steady while turning the packing nut clockwise with a second wrench.
  3. Confirm the Leak Stops. Turn the valve handle back and forth several times to distribute the internal packing. Wipe the valve stem dry with a paper towel and watch for any moisture beads to form.
  4. Extract the Valve Stem. If tightening the nut failed, shut off the main water supply to the house. Use your wrench to fully unscrew the packing nut and pull the handle assembly straight out of the valve body.
  5. Swap the Worn Seal. Examine the rubber washer at the end of the stem or the packing cord around the shaft. Replace any cracked or flattened seals with new components of the exact same size.
  6. Reassemble and Pressure Test. Slide the stem back into the valve body and tighten the packing nut until firm. Turn the main water supply back on slowly and inspect the valve for any signs of seepage.