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It shouldn’t be necessary to turn off the water to the entire house just to fix a leaky faucet, but that’s exactly what many homeowners must do. Why? Because they don’t have individual shutoff valves installed under every sink. 

If you’re facing the same situation, consider putting a valve on every hot- and cold-water supply tube. The valves will not only allow you to shut off the water to one sink without disrupting the flow to others but they’ll also provide a quick way to turn off the water in the event of a flood caused by, for instance, a cracked fitting or ruptured supply tube. The good news is that adding compression shutoff valves to an existing sink is a simple, straightforward job that most homeowners can handle. In most cases you won’t even need to replace the supply tubes that run from the valves to the faucet. However, if the tubes are corroded or kinked, replace them with braided stainless-steel supply lines (about $5 each). Standard compression valves cost about $7 each.  

Two conditions, two valves 

There are two styles of compression valves commonly used in sink hookups. When the water pipe enters the sink cabinet through the back wall, a right-angle-stop valve is required to make the 90-degree turn to the faucet. When it enters through the floor, no turn is needed so a straight-stop valve is used. 

You must also consider the type of pipe that supplies water to the sink. If it’s made of half-inch rigid copper, you’ll need a compression fitting to connect the valve. If the piping is threaded galvanized iron, use a valve that has female iron-pipe threads. Here, we’ll show two different installations: adding an angle-stop valve to galvanized iron pipe and putting a straight-stop valve onto copper pipe. Note that angle- and straight-stop valves are available for both copper and iron piping.  

Angle-stop valve 

Your first step is to shut off the water to the entire house at the meter. Drain the system by opening the sink and tub faucets on the lowest floor. Some water might remain in the system, so keep a small bucket handy. 

Next, use a wrench to loosen the water-supply tube from the adapter. Break the 3-eighths-inch compression nut free with the wrench, then twist it off with your fingers. To disconnect the other end of the supply tube from the faucet, use a basin wrench. The long handle of this wrench allows you to reach up behind the sink bowl and grab onto the faucet’s coupling nut. With the water-supply tube removed, use a pipe wrench to grip the threaded galvanized pipe stub coming out of the wall. Then use an adjustable wrench to unthread the old adapter from the pipe stub. Clean away hardened pipe dope from the pipe threads. Brush on a fresh coat of pipe-joint compound, then thread on the new valve. Tighten the valve using the adjustable wrench, but be sure to backhold the pipe stub with a pipe wrench. Lubricate the threads of the angle-stop valve with pipe-joint compound and attach the new flexible supply tube. Connect the opposite end of the tube to the faucet with the basin wrench. 

Straight-stop valve 

Sinks plumbed with copper pipe are even easier to upgrade. In this case, we attached a straight-stop valve to the pipe stub with a compression fitting. Start by removing the water-supply tube and loosening the lower compression nut with a wrench. Lift out the old adapter fitting and set it aside. You won’t be able to remove the old compression nut because the crushed ferrule will keep it locked in place, but that’s not a problem.  

First, brush pipe-joint compound onto the valve threads and then press the valve onto the pipe stub coming through the floor of the sink cabinet. Next, pull up on the compression nut and thread it onto the valve. Finish tightening the nut using two wrenches; be careful not to overtighten the nut, or the fitting will leak. 

Finally, reconnect the supply tube to the valve and faucet, then turn the water back on. If you find a slight leak, tighten the compression nut a little more.