radon in water
No, UV light will not address radon. I would suggest you do a long term air test (takes about a month) in the lower level of your home to see if radon is an issue in your house. Radon in water is a problem when it aerates into the air (through shower or faucet). Testing for radon in water is difficult too. If treatment is necessary, you will treat with aeration of the air in the lower level.
Hope this helps!