Even though your iPhone may be under warranty, Apple will not replace it if there is water damage. In the iPhone there are 4 sensors, two of which you can see. The first visible sensor is the earpiece hole. The second one is located at the bottom middle separating the connector. If you shine a light on these then look at any of the two sensors, they will have turned pink if the iPhone came into contact with water. If either of these sensors is pink, Apple will not replace the phone.
We can typically save about 50-60% of the phones that come in to us for water damage. The cost varies depending on the damage done. For $35.00 we can run diagnostics on your iPhone to see if we think it can be saved. If we cannot repair the damage then we normally have high quality used iPhone that you may purchase at affordable prices. The $35.00 will be applied to the repair cost.
* Listed above is advice only for saving a phone subjected to water damage. This is not a guarantee of success. Water damaged phone that we repair are not eligible for our limited warranty.