Say I shutoff the water at the main of a 2-story house. I open a faucet on the first floor. How long should it take for the water to stop running from that single faucet?

Will ALL the water from the second floor need to be emptied through that faucet before I can begin work on the plumbing? I noticed it takes a minute or two for the faucet to finally stop running. Is this to be expected? I've mostly only worked on 1-story houses where shutting off the main, then opening a fixture will almost stop immediately.

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    Because in the past case, the water was hydro-locked, it didn't continue to drain because the plumbing was intact, so no way for air to get into the system. In this case, an upstairs valve has a leak, so air is backflowing into it at the leakage rate, allowing a corresponding amount of water to trickle out downstairs. If you threw open ALL valves, the system would drain both faster and more completely. – Harper - Reinstate Monica Sep 10 '19 at 23:26
  • Are you also opening faucets on the second floor (to let air in to replace the draining water)? – Ray Butterworth Sep 11 '19 at 1:00
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    It may be a false assumption that the system has to be entirely/thoroughly drained before beginning work on the plumbing. Work involving threaded, compression, or crimped connections can be done wet. Solder/sweat work must be done dry, but when there's a persistent nagging trickle of water, it may be dealt with by use of a dissolvable sponge. I use a piece of fine texture white bread for those cases. Remove as much water as possible by shaking the pipe, sucking through a drinking straw, or using a wick (paper towel), then poke a piece of bread into the pipe and do the solder work quickly. – Greg Hill Sep 11 '19 at 14:57
  • You can expect a slow drip for a long time; no problem unless you are soldering copper. Bread pushed into a copper pipe will stop the drip for soldering, the water pressure then breaks up the bread. – blacksmith37 Sep 11 '19 at 14:59
  • @RayButterworth No I didn't open any of the fixtures on the second floor, that was probably causing the slowdown – invulnarable27 Sep 12 '19 at 4:54

Yes, all the water will drain from the second floor. It will take awhile because the faucet you're opening probably has an aerator on it which restrict flow and you only have gravity as a flow force. When working on a one story house the pipes, for the most part, are all horizontal so gravity isn't a factor.

You can speed up the draining on two story building by opening more faucets, some on the second floor and ones without aerators.

Don't forget, you have to drain the hot water pipes too.

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The water did shut off successfully. The pressure did pop off in a fraction of a second. Or, if you have a leak in the system, it disappeared in a couple of seconds - too fast for you to find a faucet and open it.

Why did it not run in the previous house? Because the water system was fully sealed, and vacuum locked. Water couldn't fall, because if it did, there'd be nothing to replace it. It would leave a complete vacuum (like the vacuum of space), and that requires 32 feet of "head".

Why is it running in this house? Because of the leak. Opening a lower faucet means you now have two openings in the water system - the opened faucet, and the leak. Air is now backfeeding through the leak at a certain rate, and water can fall only that fast. That's why it's taking a long time to empty.

There's one more reason it may seem to take a long time. Water main valves are rarely operated, and so they often "mineral up" to where they can't completely close. So even with the main closed, water will keep seeping into the system. If you're trying to solder, those are tough.

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