Why Do Pipes Burst?

There are a couple of factors to think about when answering this question. The most important contributing factor is the expansion of water when it freezes. If the pipes are weak or faulty in any way, this may cause the pipe to burst more quickly than it would otherwise. Modern plumbing systems often use pipes made of plastic compounds that will also break more easily when subject to pressure from the inside.

Let’s address the idea of water expanding as it freezes. Most of the iron and copper pipes of the past were strong enough to stand some pressure from freezing. Even PVC/plastic pipe can take some of this stress. But when the freezing process goes beyond safe limits, there is little to stop the material from rupturing. When the water thaws, serious damage is likely. Simply put, pressure from expanding ice and the added pressure of liquid water backing up cause too much stress on the pipe.

*Tip – keep a small trickle of water running through pipes in cold weather, when the faucets won’t be used for awhile. Shutting off the water at the source and opening the faucets may also be a good idea. Water that we use to bath and shave is generally safe to take internally, of course. But all water supplies contain some impurities that actually help water freeze more quickly than it would if completely pure.

According to the International Association for the Properties of Water and Steam most liquids behave in similar ways when cooled and heated. When liquids are cooled they shrink (contract). Molecules are moving more slowly and move closer together due to natural forces. When the liquid reaches freezing temperature, the crystallized solids are packed together tightly.

Water is an exception to this natural rule. Water contracts somewhat when cooled but at a certain temperature it begins to expand. This is due to what IAPWS calls “the structure of the water molecule.” Water is made of oxygen and hydrogen. Hydrogen bonds get stronger at lower temperatures but the crystalline structure is “very open.” Ice is less dense than water and this open nature of ice allows some life forms to continue to live in ice or very cold water.

If we were able to look at a molecule of liquid water and a molecule of frozen water (ice) we would see that the individual parts are packed much more closely together in the liquid state. Ice forming inside any restricted area produces tremendous force, as we can tell from burst pipes, concrete slabs that are pushed up when groundwater freezes and so on. Scientific studies have shown that a volume of water expands 10 percent or more when it reaches the freezing point. So, if a pipe is full of liquid water that is able to move on through the system there are no problems. The same amount of space given to the liquid water is not large enough to hold the ice when this water freezes. It’s simple yet fascinating.