What is the principal source of excessive lead and copper in a customer's water?

The principal source of excessive lead and copper in a customer's water is the corrosion of household plumbing. In many cases, homes constructed with lead solder or lead pipes, or those that have copper pipes with lead solder, can experience leaching of these metals into the drinking water. The corrosion process is often influenced by the water's chemistry, such as pH, temperature, and mineral content, which can cause these metals to dissolve into the water supply, especially if the water is soft or acidic.

This is a significant public health concern as both lead and copper can have harmful effects on human health, particularly in children and pregnant women. In contrast, the other options cited—industrial waste, pesticide runoff, and surface water contamination—are less direct sources of lead and copper in household drinking water. While they may contribute harmful substances to the broader water supply, they are not the primary means by which these specific metals are introduced into the water that families consume at home.