steam drillers, page-18

The radiogenic heat occurs throughout the rock mass and the byproducts stay where they are as Neil has already pointed out. At interfaces the only daughter product that could move is the radon gas. While this is radioactive, the various isotopes that could be produced have half lives of just a few seconds to a few days (mostly at 4 days), so that there can be no significant build up of radio activity. Radon is also inert so that it does not normally chemically combine with anything.

Do you sleep in the bedroom of a brick house? Then you will be breathing the radon molecules that exude quite naturally from the walls. We seem not too concerned about that. (Or should that be the scapegoat for all the evils in society?)

It would be quite safe to drink the water (deplete of kinetic energy).

Juke