Why does "dripping the water" work?

In places of the world where the temperature drops below freezing, but not too terribly below freezing, we’re told to let the water drip on our faucets to keep the pipes from freezing.

Why does this work? And wouldn’t it be useless below a certain temperature?

I have upstairs shower/bath plumbing that will freeze when the temperature outside is below zero f. It only takes mere drops of water flowing, not even a stream. It works because the water, however slowly, keeps moving and not just collecting there freezing.

Because the water from whatever source it’s coming from is well above freezing, so it will heat the pipes as it goes past and not drop to freezing as it moves.

Yes, it will fail with sufficiently low temperature.

Flowing water doesn’t freeze. (That’s not completely true, but close enough.) Depending on the temperature, you might need more flow to stave off freezing.

Wait. Heat the pipes? Are people who are in this situation supposed to be using their hot water? I’m vaguely aware of this advice, though admittedly fuzzy on the details because here cold-weather is factored into home building so an extended winter power failure is about the only time this is a worry.

It also helps relieve the pressure IN the pipe. It’s the pressure that cracks pipes, so if there’s an outlet at the farthest end of the system the pressure won’t build.

This is kinda cool video:

Not hot water, generally; usually freezing issues occur before the water heater. But the service pipes for water are set below the frost line, so between the source and the point where it comes up to your home, it never gets cold enough to freeze; so compared to the last few feet, the water being let through probably IS heating the pipes, along with the flow making the water less likely to freeze.


Source: too many damn hours spent under a trailer house with a heat gun or propane torch thawing the pipes… Glad I don’t have that problem any longer.

No. Say the water from the source is at 45 degrees F. The pipes are exposed to 10 degrees. If the water is flowing, it is constantly pulling 45 degree water thereby “heating” the pipes.

If you ran hot water, you would just be pulling from you internal water heater to another part of your house. It would draw the outside water into your hot water heater, but for the purposes of the thread, would be no different that running cold water.

Everything above absolute 0 has some heat in it. The water flowing into your house is above freezing, and it will heat things that are colder than it (like your pipes in the uninsulated crawlspace) by conduction.

C’mon, alla yez! Everyone knows flowing water won’t freeze due to the friction generated by the H2O molecules bumpin’ up against each other.


Yeah, that’s way rivers never freeze.


Keep in mind that it may not be sufficient to drip just a single faucet. Pipes snake through your house. Dripping a single pipe will keep the water moving between the water main and that faucet, but water in other pipes will be stagnant. Try to drip enough faucets so that all pipes that move along the outside walls have water moving through them. Kitchen sinks are commonly against an outside wall, but also consider bathroom plumbing which may also run along outside walls.

It’s the fish farkle that freezes!


my understanding is that this not ‘also’ but the main reason pipe burst. Opening the tap allows the ice to expand without building catastrophic pressure

Since homes have both hot and cold water lines running to sinks/baths do you need to get that ‘drip’ to be pulling on both lines? I know a sitting hot water line will start off hotter than the cold but can’t it cool off to below freezing over time if it sits?

I could be missing the joke. But since we’re in FQ, there’s a huge difference between rivers freezing completely to the bottom and just surface freezing.

Even Lakes Superior, Huron and Erie have completely frozen over at some time since 1900, but the deeper Lakes Michigan and Ontario never have.

Pipes exposed to low temps freeze from the inside->in. Keeping a flow prevents the inside from becoming stable enough to add to existing ice crystals, below zero, because the city water is, of course, liquid. Or something (waves hand).

This seems much more likely than the other answers given here. The extra heat introduced by a slow drip isn’t going to be significant compared to the exposure of a bunch of copper pipes to below-freezing temperatures, nor does the flowing theory make sense to me. But if you relieve the pressure, the pipes are able to freeze–just without bursting the pipes.

For those of you that have used the dripping water trick in deep freezes: have you ever noticed the rate of flow (with a wide-open faucet) drop after a long freeze? If so, that might imply that the pipe has partially frozen, constricting the flow–but due to the pressure relief, hasn’t damaged the pipe.


And not just water, we have underground oil and gas pipelines that show the same behavior. Their temperature is the same year around, not matter if it is snowing or summer.

Look at Fig 1, in this publication for Edmonton, Canada. You can see the wide fluctuation in Air temperature, but the underground temperature is pretty constant all throughout the year


Yeah, flowing water inside of a house won’t normally freeze. A waterfall is a different story. :grinning: