Water has a unique property in that it expands as it freezes. This expansion puts tremendous pressure on whatever is containing it, including metal or plastic pipes. No matter the "strength" of a container, expanding water can cause pipes to break. Pipes that freeze most frequently are those that are exposed to severe cold, like outdoor hose bibs, swimming pool supply lines, water sprinkler lines, and water supply pipes in unheated interior areas like basements and crawl spaces, attics, garages, or kitchen cabinets. Pipes that run against exterior walls that have little or no insulation are also subject to freezing.