Motors are fine in water (except sensored brushless).
Receivers usually just require drying out before they'll work again, although a lot of water in a receiver can make all the dust and muck stick together to make a gunge that needs to be flushed out.
ESC's are the main problem with water, they all go bang, and I only know of a couple that I would trust to work properly in water.
Trust me, we know a lot about racing in the UK in the wet
And also frost;