So it finally happened to me too, I dropped my phone into water. Even though I acted with the speed of a lion chasing the wildebeest, grabbed my phone and pulled it out of water within a few seconds, the water seemed to seep into some parts of the phone. With such a water damaged phone, the first thing you have to find out is whether the battery has suffered water damage. Because if you try to put the battery on charge, it can cause unwanted reactions inside the battery and it may explode.
The phone battery manufacturers make it very convenient for the phone users to find out if the battery has been damaged because of water using a color coded sticker. You can find this small rectangular or circular sticker on your battery. This sticker is very small and is often close to the battery terminals. The sticker is either white in color or has pink/purple hatching marks.
When this indicator sticker comes into contact with water for some specified time duration, it changes color and becomes solid purple or pink in color. The color does not change instantly, so if you quickly pull out the phone from water and dry out the battery it will perhaps not get damaged. But if the battery stays inside the water for more than a couple of minutes, the color changes and the battery can be assumed to be damaged.
You should not use such a damaged battery and replace it with a new battery bought from the manufacturer of your phone. At the same time, you should also not use a wet or damp phone, but wait for it to dry out. One quick way to dry a phone is to put some of the dry ethanol inside it which makes the water evaporate faster from the phone. For more drying up, you can put the phone covered up inside a bowl of uncooked dry rice for a day or so.
Conclusion: You should not use a water damaged phone battery as it can cause some fire or explosion while trying to charge it. Phone manufacturers make it pretty easy to find if the phone battery is water damaged or not.