If you only read the first post, you should read this post as well:
https://www.backyardchickens.com/threads/debunked-toxic-levels-of-lead-in-black-rubber-feed-bowl-water-30-mg-l-2000-times-epa-limits.1620309/page-5#post-27692783
And maybe these two, that came before and after it...
You can be a lot more sure where the lead is coming from if you do two more tests:
--water from the well (collected in some container that should be lead free)
--water from the well, after it sits in the black rubber bowl (using the very same water you just tested, poured into the black rubber...