today our snow is melting and i just ran my mm E-maxx through 4" slush and to see how it would work i drove it through a 6"-8" puddle of water multiple time going fast and slow. The only thing that seems to be effected is the receiver.
The boards are coated to make them water-resistant, but certain connections are exposed and your connections may oxidize over time. And it's probably not good for the USB port.
Besides, shouldn't you have asked this question before you ran it in water?
it is "water resistant". The boards are coated, which makes them resistant to water, but castle does not claim them to be water proof, exactly. There's some info about it in the FAQ on catle's site.