Radon mainly effects the lungs and requires continued exposure. I still personally would not expect a radon rich spring to be healthy, even with short term exposure. The effects of radon exposure over time on the lungs are well studied. Anecdotally, the primitive way to determine radon presence in a home without the use of sensors is to look at the number of scratches on a window. Radon causes them.
Our local library has a Radon detector you can borrow. We did. No Radon...
AFAIK the scientific consensus is no amount of radiation exposure is beneficial. There have been some theories going around about how a small amount of radiation can be beneficial but I think that's been proven not to be true.
The consensus does not exist. The LNT model is convenient because it lends itself to easy measurement, and extremely low radiation exposure (e.g. non-nuclear work on a submarine) can't be tied to any specific risk. You wouldn't want an occupational health organization behaving in any other way.
On the other hand, LNT utterly fails to address the well-documented trend that people in areas of high background exposure experience lower rates of cancer. The mechanisms of this effect are not understood, though often hypothesized, nor is there any strong argument for a particular upper limit (though plenty of known examples, like smoking and frequent flying, lie beyond it.)
I wouldn't advise anyone microdose on radon, nor ignore the risk of radon if you're in the habit of keeping your modern home closed up... but this matter is not settled as you portray.
Edit: sorry for my other flippant comment. The confident misunderstanding of science got me a little worked up.
I have one, and a sub slab Radon abatement system. My levels were pretty high for a basement and that was how I learned about Radon. You're 100% correct about that there is no safe level of Radon exposure. The international community decided on "safe levels" because the cost of abatement is far and away from what many countries can afford, but I think they're moving to the "no safe levels" definition this year.
You don't. "No safe levels" just means it'll be a health factor because there is no benign amount of Radon. The lowest my house gets is .4 due to ambient Radon, that just is what it is. The only thing you could do is move to somewhere that there's no Radon ATM.
