Main water shutoff valves can become clogged with mineral deposits and grit, causing slow leaks. With the right materials and correct procedure, it's a safe and easy repair.
Mineral deposits and tiny pieces of grit can gradually build up in an old gate valve, making it impossible to fully close.
Shut off the street-side valve where the water enters the house. Then loosen the coupling nut and remove the nipple from the old valve.
Screw on the new ball valve, install the old nipple and the new leather washer (use Teflon tape or pipe dope on the threads). Tighten the coupling nut, turn on the water and check for leaks.
Old-timers prefer leather washers, which will last longer than neoprene washers.
If you get drips of water coming through your pipes even with the main shutoff valve completely closed, it's probably time to replace the shutoff with a new ball valve. It's not complicated, but the house water will be off, so it's a good idea to get your ducks in a row before you start. To remove the old valve, you'll have to undo the coupling on the “house side” of the water meter. There's usually an oil-impregnated leather sealing washer inside the coupling. Leather washers are tough to find, so look at a plumbing supplier or check for them online. Some plumbing suppliers sell neoprene washers, but the “oldtimers” swear by leather, because eventually neoprene will dry out and crack. You probably have a 3/4-in. pipe leading to and from the leaky valve. Buy a threaded replacement ball valve; it's a far better choice than the older gate-style valve.
Test the “street-side” valve where the water enters the house. Since that valve is just as old, test it to make sure it closes all the way and reopens again. If that valve needs replacement, contact your water utility to shut off the main valve at the curb.
Then check out the electrical system “bonding jumper” that runs from a clamp on the house side of the meter to a clamp on the street side. If you can unscrew the old valve with the bonding jumper wire in place, fine. If you can't, do not disconnect it. The safe way to work around this problem is to install a longer section of copper wire and two new clamps (6AWG for 100-amp service, 4AWG for 200-amp service). Then remove the short bonding jumper. At that point, you're ready to shut down the water and replace the valve as shown.
Have the necessary tools for this DIY project lined up before you start—you’ll save time and frustration.
Avoid last-minute shopping trips by having all your materials ready ahead of time. Here's a list.