The water damage is caused when the phone has slipped in to water or some liquid had spilled on the phone or even due to the excess moisture. This could create many issues like phone doesn't work, phone doesn't charge , phone gets heated up while in use, display do not work, touch doesn't work. If your iPhone is completed dipped in water then do not try to charge it or try to switch on it, If it's ON put it OFF and bring it to us.
The expert team in iPhone service center is here to help you resolve the issues and give you a well serviced iPhone. If phone wasn't dipped in water fully then you might need to OFF the phone and let it dry, you might need to wait for a day or two. Once the water is dried from the phone you can ON it and see if the working properly else it might need further diagnosis to check if any other issue is there with any of the components.