Water: Coin devices are water resistant but not waterproof. If you spill your coffee or juice box on your Coin, it's probably no big deal. If you put it through the washer or take it swimming, your Coin will likely cease to function as designed.
Magnets: Normal magnetic exposure (wallets with money clips that use magnets) won’t harm your Coin. However, if your job or hobby puts you in close proximity to above average strength electro-magnets, this will most likely render your Coin inoperable.
Coin will not be damaged going through a standard metal detector or x-ray machine.