What can happen if your skateboard gets wet?
You should try and avoid getting your board wet at all, watch out for puddles and don't skate in the rain, but If your skateboard gets wet there are a number of things that it can affect, so you need to dry it out ASAP.
When your deck gets wet, it can cause the lamination to peel or bubble, this is what is called delamination. This isn't covered by your warranty as it is not a deck fault, liquids cause this to happen (if it happens without being caused be a liquid than it could well be a warranty issue, it's usually obvious if it has been wet or not).
Water can cause the wood in your deck to soften which can in turn lead to warping. Even once it's dried out, this will affect the performance of your deck, you will generally find it won't have the same pop that you are used to, and will often bend or break easier.
Rust affects just about everything besides your deck and wheels. Water can cause your deck bolts to rust, it can also cause your trucks (particularly the axles) to rust, and most notably it can cause your bearings to rust and bring in extra grime.
Rusty bolts and trucks/axles can ultimately lead to breakage, but that can be a slow process and isn't going to be a big worry, especially considering they will generally dry out quick enough that it shouldn't be much of a problem. The more serious issue is the bearings. When water gets inside the shields it can take a long time to dry, which does cause rust. If they get wet, open them up and dry them out ASAP to try and avoid potential rust. If they start to get noisey and feel rough when they spin or don't spin freely, it's possible that they are starting to rust (or are really dirty). You don't want this. If they are just dirty, you can clean them, but if they are starting to rust it's permanent damage. If the rust isn't bad you can try cleaning them with a rust eater, but your bearings will not be as round or smooth as they were, which means they will not perform as well.
The best solution is to avoid water altogether, it will keep you going for longer, and water damage isn't covered by warranties, so keeping your skateboard dry will save you money too.