Our local 4-H club will analyze it for free. Right down to mineral and microorganism count.We're on city water here but a relative's property has a well that we visit. I didn't know you had to check them. Who tests for it?
I would not trust these guys as far as I could squat launch them, but they have uses:
https://www.epa.gov/radtown/natural-radionuclides-private-wells
https://pubs.usgs.gov/fs/2000/0012/
http://www.idph.state.il.us/envhealth/factsheets/radium.htm
Funny thing, this wasn't an issue until about a decade ago, which tells me it is not natural.