Because the source of lead and copper is generally the customer-owned piping rather than any part of the water supplier's plumbing, equipment, or even the original source of water, the Lead and Copper Rule is quite unlike any of the other provisions of the National Primary Drinking Water Regulations. To some extent, the water supplier is made responsible for the quality of water sampled at pipes and locations completely out of the supplier's control. The most unusual features of the rule follow from this difference.