Introduction: Leave the Water on While Working on Old Plumbing

If you are working on older plumbing, it is often difficult to turn off the water shut-off valves under the sink or behind the toilet because:

1. The valve is corroded internally and stuck in the open position.

2. The handle has nearly corroded away and it crumbles in your hand when you try to turn it.

3. You are like me and you are afraid that if you close the shut-off valve, it will begin to leak when you open it again.

4. All of the above.

To be sure, you can turn the water off at the street, do your repair quickly (replace the faucet washer or replace the toilet flush valve) and then turn the water back on. But if the repair is going to take more time, say, because you are having new counter-tops put into all 3 bathrooms, or you find that you don’t have the right parts, then it would be nice for the rest of the people in the house if you could turn the water back on at the street while you complete the project.

Step 1: How You Can Turn the Water Back on at the Street

So, in that situation, how can you turn the water back on at the street (without turning off the shut-off valves) while you drive to the hardware store to look for more parts? It is simple: you can either cap off the water supply lines at the shut-off valves or you can plug the flexible water lines while they are still attached to the shut-off valves.

Step 2: Capping Off the Shut-Off Valve Under the Sink

To cap off the shut-off valves under a sink, you will need to know what kind of valves you have. Remove the riser or flexible water line from the shut-off valve and inspect the connector.

A lot of older shut-off valves are 3/8” flare fittings, whereas most of the newer valves are 3/8” compression fittings. (See Photos) While it is easy to find a brass cap for a 3/8” compression fitting, it is often difficult to find a brass cap for a 3/8” flare fitting. I have found it much easier to buy a flare to compression converter fitting and then cap the compression fitting.

Step 3: Making the Flare to Compression Conversion

Note- If you buy a flare to compression converter, use some Teflon enriched pipe thread compound or some Teflon tape when screwing the cap onto the converter to keep it from leaking.

Step 4: Compression Fittings Capped Off

Above is a photo of the "compression fittings" capped off.

One caveat: when looking for valve caps in hardware stores, don't let the salesperson try to sell you a 3/8" flare fitting cap for a gas line instead of a water line. They look similar, but are totally different. It has become obvious to me that the associates often don't realize that.

Step 5: If You Can't Find Either a Cap or a Converter Fitting

And if you can’t find either a brass cap for a compression type shut-off valve or the converter, it may be easier to just buy a couple of brass plugs that will screw into the faucet connector fitting (usually ½” FIP). That is to say, the fitting on the far end of the flexible hose or the pipe that goes from the shut-off valve to the sink faucet set.

Step 6: The FIP Fitting's Gasket

Because the ½” FIP connector has a conical shaped rubber gasket inside of it, the flat bottomed brass plug will usually seal it off fairly well. Even if it drips slightly, you can place a plastic pan under the sink while you head for the hardware store or work on your repair. No matter that you might have an ounce of water in the pan after an hour or two.

Remember, these fittings are not intended to be permanent, but just to cap off the water to that fixture for a few hours or a day or two at most. They don't have to be perfect.

Step 7: Here Is the Male Plug Installed in the 1/2" FIP Fitting to the Faucet Set

Step 8: You Can Also Cap Off the Shut-Off Valve for the Toilet

Likewise, you can cap the corroded and stuck shut-off valve (usually a 3/8” or ½” compression fitting) to the toilet flush valve while you work on this fixture. These caps are usually easy to find.

Step 9: And the Water Heater...

Working on a water heater is usually not an issue because most water heater inlet lines have a more substantial shut-off valve similar to a hose bib but occasionally you will get one that is stuck in the open position. If that is the case, you can either cap the valve or plug the flexible line to the water heater. (See Photos) Capping that shut-off valve with a 3/4" FIP cap is usually easiest and that size fitting is plentiful in hardware stores.

If that fitting is not available, a brass plug for a 3/4" FIP fitting can be used to plug the water heater supply line.

Step 10: What About Showers and Tubs?

Unless you have some hidden shut-off valves in a wall or cabinet, I don't know of a way to cap or plug the water supply lines to these devices. Most tubs and showers do not have shut-off valves to the faucets or mixers. You will just have to turn the water off at the street and work as efficiently as you can while you replace the O-rings, packing, or mixer cartridge.

Step 11: In a Perfect World...

I realize that in a perfect world, I would not be facing the dilemma described in the opening paragraph, because I would have already replaced these ancient shut-off valves with modern push-fit ¼ turn ball valves- such as SharkBite style fittings.

But, alas, I live in a house where the stub-out (the amount of pipe protruding from the wall) on my old shut-off valves is not very long or the pipe behind the valves is covered with thick paint and clumps of solder. And the SharkBite style fittings require an inch of clean pipe sticking out of the wall once the old fitting has been removed.

Furthermore, I do not relish the idea of expanding my small plumbing project/repair into cutting out the sheet rock behind the old shut-off valve, replacing the pipe AND the valve, and then repairing the sheet rock.

Yes, this tutorial is a quick and dirty solution, an expedient, in a less than perfect world.