Using cloud chambers you can see that you are being bombarded by cosmic radiation from stars around the universe right now, even inside your home. Cloud Chambers (WikiPedia)

And these rays are serious radiation like electrons and protons at beta, alpha, and gamma rays. Much more dangerous than elctro-magnetic fields. But is is true that RF especially at certain frequencies like 2.4Ghz can make water molecules vibrate. This is how your microwave oven works, and if the water got hot enough it could denature some DNA and potentially cause cancer if your immune system didn't catch it and it deformed into a living form of some type.

Really strong magnets can actually drag the iron in blood through living cells causing damage. So, magnet therapy is a potentially bad idea.