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?
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.
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.
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.
