What material is discouraged for underground water lines due to corrosion issues?

Galvanized steel is discouraged for underground water lines primarily due to its susceptibility to corrosion. Over time, the protective zinc coating that initially helps resist corrosion can wear away, especially when exposed to moisture and soil conditions. This leads to rust formation and ultimately the deterioration of the pipe, which can result in leaks and compromised water quality.

In contrast, materials such as PVC and CPVC are plastic types that do not corrode, making them more suitable for underground installation where water lines are likely to encounter moisture and other corrosive elements. Copper, while durable, can also be prone to corrosion under certain conditions, but it is commonly used and treated specifically for such applications, which is why it is not as widely discouraged as galvanized steel.