Water damage often damages the iPhone beyond fixing. It sounds like you have done the correct things to attempt to avoid issues, however it appears it was already damaged.
Your warranty is voided by exposure to water. There are two sensors in the iPhone which are white, and turn red or pink when touched by water. If it has been damaged, you would need to replace it.
Repair coverage? - Check your Service and Support Coverage - https://selfsolve.apple.com/agreementWarrantyDynamic.do. This will also show the make and model of the device.