There is no reason a water dunk should hurt the FOB. Electronics are not generally harmed by water, but can be harmed by junk in water, and also by corrosive acids. The parts that are sensitive are unsealed switches and potentiometers and unsoldered contacts. The FOB has switches that could be harmed by dirt (in the water), but can easily be rinsed clean with water (and it does not need to be distilled, but if this happens a LOT, then the minerals in tap water may eventually be a concern). The battery contacts can corrode, but a simple rubbing with a pencil eraser (contacts and battery) after they get wet should keep them safe. The FOB has no pots or other exposed parts that would be hurt by water.

If a piece of electronics gets wet where it isn't supposed to, just unplug or remove all batteries, rinse throughly (even if the original water exposure was clean water, it may have moved internal dirt and dust to places it should not be). If all surfaces are not easily accessible, disassembly and/or forced air blowing may be useful.

Your concern is dirt in switches and pots and on contacts, and rust/corrosion of all metal. Dirt can cause shorting (or just lowered resistance) across leads, and corrosion can cause leads to separate (electrically). Cleaning and drying are the best repair 99% of the time.

Most low voltage electronics will operate fine under water! Clean water is not conductive. However, the RF signals sent and received by the FOB probably will not penetrate very deep water well! These are high frequencies that are attenuated by water.

-- Alan