Do you mean the receiver is ruined, or the transmitter?
You say water damage, so I presume you mean the receiver in the truck, not the transmitter in your hand.
Yes, you can buy a new receiver. Find one on ebay, then you just bind it to the transmitter. (if it's 2.4 GHz)
If it's an old AM receiver, it needs to be on the same channel as the transmitter. (or you need to get a new crystal for your transmitter to match what's in the receiver)