If your phone gets water inside it, the most important thing to do is remove the battery as soon as you can. The longer you leave the battery connected, the more likely the phone will not be recoverable.
I've saved several phones from water damage, but two I could not save had non-removable batteries. As the water dries, the ionic concentration increases and the conduction path becomes less resistive. This can short out and damage sensitive electronics. As water sits on the metal, more ions can dissolve in the water, increasing its conductivity.
If you drop your phone in the swimming pool, immediately take the battery out. Then rinse the phone in pure, fresh water. It's important to get the chlorine out because chlorine can corrode parts in the phone. The same goes for dropping your phone in the ocean. Salt water will also corrode the phone.
There are several ways to dry out your phone.
1. Forced air heat. Put the phone on a heat register on the floor in your house, overnight. This works great in the winter when the heat is on, but you'll have to find a different way in the summer. You don't want to get the phone too hot, otherwise, you can damage the phone. I wouldn't want to go over about 140F. That's about as hot as leaving it in the car on a hot, sunny day (but not on the dash).
2. Heat. A friend of mine told me how he dropped a phone in the lake, then took the battery out and threw it in the glove box. This was in the summer. A week later, he opened up his glove box, put the battery in, and the phone worked.
3. Vacuum pump. If you put the phone in a vacuum, the water will boil off at room temperature. This is great if you have access to a vacuum pump. Here's a picture of my setup, complete with a phone in the jar. This vacuum pump is made to evacuate air conditioners.
For my vacuum setup, I just found a wide mouth canning jar with a lid. I just drilled a hole in the lid and put a connector on it and sealed the threads with RTV. You don't need to screw the lid on because the vacuum holds the seal.
4. I've heard many people say to put the phone in rice (or another dessicant). Rice will absorb excess humidity. But this depends on the evaporation rate. Plan on leaving it there for at least a week before trying it again. I've never tried this method, so I don't know what the success rate is. Your biggest enemy here is time. The longer you have water in the phone, the more time it has to corrode.
The main problem with water getting inside the phone is that it will create conduction paths that may overload a circuit. I took an iPhone apart that was dropped in water a month or so before. Since the battery wasn't removable without a pentalobe screwdriver, it remained connected. One of the chips on the main board was visibly damaged from the chip inside overheating due to being shorted out.
One important thing to remember is that as the water evaporates, the ionic concentration increases, reducing the resistance. If you put the battery back in before the water is completely dried out, you may destroy the phone.
Now wouldn't it be nice if cell phone manufacturers would waterproof the inside of their phones? Or at least, sell the option for waterproofing?
