The EPA estimates that nearly half of America’s water heater installations may have been incorrectly labeled as being “non-polluting,” which means that they are not required to use a mercury or arsenic-free water source.

But that doesn’t mean that they don’t have to meet EPA’s standards for water heater performance, and it doesn’t include the potential for corrosion that could lead to leaks.

This article has been updated to clarify the role of the EPA’s Lead and Copper Rule.