It may just be my perception, but it seems like water main breaks (at least in Pittsburgh PA) are more common in the winter during the cold weather. It may just that they are more news worthy in the winter (water+cold=ice > news).

Are water mains more likely to break in the winter? If so what can be done to limit or prevent the occurrence?

  • $\begingroup$ In the absence of historical data to back this up, I'm skeptical. There are plenty of cases of mains here in Eastern MA breaking in the spring or summer (due primarily to age). $\endgroup$ – Carl Witthoft Feb 21 '15 at 1:56

Cold makes things shrink. Despite being buried — presumably below the frost line — both the ground outside the pipe and the water inside the pipe are much colder in winter than in summer. This causes the pipe segments to shrink, putting tension on the joints, and increasing the chances that a weak one will fail. By contrast, warm weather puts the joints under compression, helping to seal any leaks.

Also, the ground does shift during freeze/thaw cycles (a.k.a. "frost heaves"), and this can cause additional stresses on pipes, even below the frost line — especially if an old leak has washed out some of the soil supporting the pipe.

There's really nothing that can be done that I know of to mitigate this for existing pipes. Any preventative measures must be put in place when the pipe is first installed. For example, putting a layer of crushed stone around a pipe helps to decouple it both mechanically and thermally from the surrounding soil.

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    $\begingroup$ Cold also makes many materials more brittle, especially steel, and thus prone to failure. $\endgroup$ – Ethan48 Feb 20 '15 at 15:47
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    $\begingroup$ Also very important in this is that water, unlike just about EVERYTHING ELSE in the universe, expands as it gets colder, specifically from 4°C down. So while the pipe around it is contracting, the water is expanding, exerting even more pressure. $\endgroup$ – Trevor Archibald Feb 20 '15 at 16:05
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    $\begingroup$ @TrevorArchibald: The pressure of the water inside the pipe is regulated by the utility; the temperature of the water has nothing to do with it. And the whole idea of putting pipes below the "frost line" is that they stay above 4°C anyway. $\endgroup$ – Dave Tweed Feb 20 '15 at 16:40
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    $\begingroup$ @Dopeybob435: I have never heard of a water main freezing solid (across its full diameter), which is what would be required in order to create a pressure problem. Do you have any evidence of this occurring? $\endgroup$ – Dave Tweed Feb 20 '15 at 17:32
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    $\begingroup$ Public water service wise I don't have personal experience with them freezing solid however other jurisdictions have. Just to split hairs, I don't think the pipe needs to be frozen solid for ice expansion to compromise the piping, it just needs to bridge a large portion. Incomplete example list: startribune.com/local/west/245699131.html, minnesota.cbslocal.com/2014/04/14/…, wi-weston.civicplus.com/DocumentCenter/View/1582 $\endgroup$ – Dopeybob435 Feb 20 '15 at 17:56

Water main failures are greater in the winter months than in the spring or summer. As a water utility professional in northern Illinois we have around 120 failures each year with 20 + years of data. Each and every year we have 90 of the 120 between December and March (Fact). The question that indeed is hard to define is why? Here are the facts I see year after year and I base my opinion on.

  • Each year as the frost gains depth and speed 1 foot to 3 feet, between December 15th and January 7th we will have 25 main breaks.
  • From the 7th of January till the 21st of Feb. frost stays at 3 feet we will have 40 main breaks.
  • From Feb 21st till March 20th as the frost is coming out quickly 3 feet till 1 foot or less we will get 25 main breaks.
  • Many of the older pipes are made from cast iron that is very rigged and brittle. its like trying to bend a candy cane. 95 percent of failures are on this type of pipe.
  • The newer pipe is made from ductile iron pipe that is less rigged, allowing it to flex and bend with the frost speed and depth both in and out.

As far as frozen water mains the only two I have known of were both shallow 4 foot or less, a dead end run, and very few service lines on them 1 or two. I could go on and on about the subject but be it known I have been watching frost, cold weather, age of pipe, and material composition for 24 years and the whole water main failure is still a great mystery many days. Water Utility Superintendent Northern Illinois.


As far as I know, there are two major factors, fatigue loading and low temperatures.

Pipes buried below roads experience fatigue loading from traffic, surprisingly enough. Literally cars driving over the road surface imparts a load onto the pipes, even if it's a very small load. However, this happens many times every day and pipes stay in the ground for long periods of time. This means they experience millions of fatigue cycle loads over decades (50+ years isn't unusual for gas pipelines, at least).

Add in thermal cycling thanks to the weather and metallic pipes (and plastic, to a lesser extent) will become brittle under low temperatures.

You can see where this is going.

Corrosion caused by water is yet another factor etc etc etc and basically its all a surprisingly hostile environment for something which has to last so long.


Water mains don't freeze. The water pressure is regulated along the way (water towers, etc), so temp doesn't affect pressure. Frozen ground heaves, cold pipes contract and cold pipes are more brittle.

  • $\begingroup$ Welcome to Engineering. Would you care to expand a bit more on your answer, please? As currently written, your answer doesn't really address the broader question raised. $\endgroup$ – GlenH7 Feb 20 '15 at 21:02

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