That is a great question. These lines are not plastic, they are primarily made of iron; especially water lines that exist throughout the older sections of the Wilmington area where we have experienced our breaks. Here's what happens. Iron contracts when it gets cold, and expands again when it gets warm. During this contraction and/or expansion, cracks can form in the pipe. These cracks seep or gush water causing a water main break that shows via sink holes or pooling / running water above ground. The lines under your house are copper because copper expands and contracts (or stretches) well in the changing temperatures; ie no cracks. There is information about this subject and other frequently asked questions on our website at www.cfpua.org.
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