How to Install Water Shutoff Valves Under Your Kitchen Sink

Water shutoff valves under your sink are the difference between a minor leak and water damage spreading through your cabinets and floor. These small ball valves let you cut water to the sink without shutting off the entire house—essential for repairs, maintenance, or emergencies. If you have old or missing shutoff valves, or if yours don't turn smoothly, replacing them is straightforward work that pays for itself the first time you need to fix a faucet or replace a supply line. This is foundational plumbing that every homeowner should have and understand.

1. Shut Down the Source. Locate your main shutoff valve, typically near the water meter in a basement, crawlspace, or utility room. Turn the handle clockwise until it stops. Test by opening a faucet upstairs—water should stop flowing. If it doesn't, or if you can't find the main valve, contact your water company for the external shutoff location.
2. Release the Pressure. Open the kitchen sink faucet fully, then open a lower faucet (bathroom sink or outdoor spigot if available) to bleed pressure from the lines. Water will drip for a few seconds, then stop.
3. Catch the Water. Slide a shallow bucket or pan under where the supply lines connect to the sink. There will be residual water in the lines—usually a cup or two. Position the bucket to catch drips from both the hot and cold supply connections.
4. Disconnect Both Lines. Using an adjustable wrench, hold the nut on the underside of the sink fitting with one wrench while turning the compression nut on the supply line with another wrench. Turn counterclockwise to loosen. Do this for both hot and cold lines. Once loose by hand, unscrew the rest of the way and pull the supply line away from the sink. Tip the line into the bucket to drain remaining water.
5. Strip Away the Old. If old valves are already installed on the wall or on the inlet pipes coming down, you can replace them in place if the pipes are rigid copper or steel. If the pipes are flexible supply lines attached to old valves, cut or unscrew the old valves off the incoming water lines using a wrench or hacksaw. If there are no valves at all, you'll install new ones on the incoming supply lines.
6. Square Cut Copper. The supply lines coming into the cabinet (usually from the wall or floor) should be stubbed out 4–6 inches below where the sink lines connect. If you have rigid copper tubing, cut it square with a hacksaw or tubing cutter, then deburr the cut end with a file or reaming tool. If you have existing PEX or flexible supply line, leave it as is. For iron pipe, you may need a pipe wrench to remove old fittings.
7. Seat Both Valves. Slide a compression nut and ferrule (ring) onto the incoming supply line, then slide the compression nut onto the shutoff valve. Hand-tighten first so everything is seated. Using two wrenches—one on the valve body, one on the nut—turn the nut clockwise to tighten the compression fitting. Tighten until snug; about a quarter-turn more after hand-tight is enough. Do not over-tighten, which can crack the ferrule. Repeat for both hot and cold lines.
8. Watch for Drips. Turn on the main water shutoff valve slowly. Open the kitchen faucet and let water run for 10 seconds, then turn it off. Inspect the compression fittings on both new valves for drips. If you see a slow drip, tighten the nut a quarter-turn with a wrench. If it still drips, turn off the main valve, drain the line, and re-seat the ferrule by backing off the nut completely, then re-tightening.
9. Reconnect the Sink. Slide the compression nut and ferrule from the sink's old supply line (or a new one if replacing) onto the outlet of the first shutoff valve. Hand-tighten, then use two wrenches to snug it. Repeat for the second supply line and valve. Turn the faucet on and off a few times to check flow and for any leaks at the sink connection.
10. Verify Quick Response. Once the sink is reconnected and flowing, locate the handles on your new shutoff valves (they should be ball valves with quarter-turn handles). Turn each one fully clockwise (off), then back counterclockwise (on). Water to the sink should stop and start cleanly. The handle should move with light pressure—never force it.
11. Label for Life. Use waterproof label tape or a permanent marker on the cabinet wall or on the valve itself. Write 'Hot' and 'Cold' so anyone in the household knows which valve controls which line. This takes 30 seconds and prevents confusion during an emergency.
12. Watch and Wait. Shut the cabinet doors and check back in 30 minutes, then again before bed. Look for any pooling water under the sink. If everything is dry, your installation is complete. If you see water, tighten the leaking fitting a quarter-turn and recheck in 30 minutes.