There is background radiation everywhere. Mostly from natural causes. If you live in a city built on granite your background radiation dose will be much higher than most. Still harmless.
What's more of a problem is radon. In some areas where the rocks contain a significant amount of radium the radon that it produces can build up in basements. This can be a very real hazard. The cure is simply ventilation.
In the UK the worst affected area is Cornwall, in the far southwest. This article is a good and sensible view of the subject:
http://www.independent.co.uk/life-st...e-2047987.html
If you live near here then your background dose is likely to be a lot higher:
https://en.wikipedia.org/wiki/Natura...ission_reactor
I don't think there's any practical way of removing radioactivity from the water supply and if it's only at background levels or slightly above there's no hazard anyway.