How do I know if my phone has water damage?

Bummer on the phone getting rained on. To know if it has water damage, remove the back cover and look just above the battery compartment. There is a 4mm square located there that should be white in color. If it is red or a reddish color, it has been exposed to moisture.

You can try and put the phone in a plastic bag with dried rice and seal the bag. Leave it in there for two to three days and see if that removes the moisture and corrects the issues you are experiencing.