Obviously the person you replied to meant "free to the homeowner". Instead of sarcastically playing dumb, you might review the HN community guidelines.

In terms of "someone else" paid for it, well yes, in every good society to live in there exists the concept of "an individual person shouldn't have to pay for this, but it benefits everyone to have it, so we will use collectively pooled resources to create it".

It's not hard to see how avoiding lead poisoning in a country's children benefits that country a decade down the line.