Not a direct answer, but there are lead testing kits on Amazon. You mail a tap water sample to a lab. The “kit” is not much more than a vial and prepaid shipping label on a small box.

Yeah it sounds amazing in theory, but none of us have the time to figure that out. It's just way too complicated. It needs to be dumbed down so that you contact one single company, they send a guy over with a bunch of kits and translates it into an easily understandable how-fucked-are-you score, with upsells for improving your score.

Sounds like a business opportunity

This kind of thing exists and is rife with head office pushing iffy practices to boost the detection - e.g. sampling a bigger area than the official measurement equation requires etc.

Lots of problems with ‘meth detection’ companies that over-detect then sell you tens of thousands of dollars of remediation services.

Do not use lead testing kits. They’re a waste of money. The best thing to do would be to find an EPA-licensed lead profession to test your property with an XRF gun. You get a breakdown of every place in your house, inside and out.