You can only test at a point in time. So you want to test periodically. Since it sounds like you are on municipal water, 12 months should be ok, 6 months if you

You can only test at a point in time. So you want to test periodically. Since it sounds like you are on municipal water, 12 months should be ok, 6 months if you're feeling paranoid. I'm on well water and test frequently. Home testing kits are cheap. Sending it out to the lab is pricey but you get more detail and consistent results. For lead, home testing is fine. You should do at least one mail lab test to start with. Unless your house is ancient, almost certainly you won't find lead. Your water company should be using "clean" sources to ensure no lithium, magnesium and such.