eli5 how does water stop radiation and not everything else outright, and how can radiation do damage to us if we are mostly made of water?

Question

eli5 how does water stop radiation and not everything else outright, and how can radiation do damage to us if we are mostly made of water?

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Answer 1

Water is dense and a flying electron hitting lots of water loses its energy quickly.

It’s like shooting a gun at the tree. Tree is big and bullet stops when it loses all of its energy trying to pierce the wood. But when you shoot the plank made of the same wood it will get through.

Amount of water in us is like a thin plank, so radiation particle don’t lose much energy going through us.