For plumbing specifically you _also_ have to worry about every link in the chain from your house to the water source. Perhaps non-intuitively just knowing if there are lead pipes because they can develop a protective sediment layer that prevents the lead from touching the water.

Anecdotally, we had a major city water line project in our neighborhood that _raised_ our lead levels because it disturbed that sediment protection.

The only real solution is testing and filtering at point of use. But even filtering is hard because most water filters sold are for flavor not for lead.