Phoenix has some of the worst water in the country. The aggressive water coming from the Colorado River and other sources is heavily mineralized and loaded with calcium carbonates — so much so that the water becomes conductive. Electric current, like water, finds the easiest path. In homes, that frequently takes it on a course through copper pipe, into the water and back out the pipe again, causing pinholing and leakage.
Calcium carbonate deposited on plumbing fixtures can ruin the finish so that it turns black. It also can destroy the inner workings of plumbing and heating equipment.