It will be difficult to ultimately know if your iPhone is suffering from water damage as the internal LDI's (Liquid Damage Indicator) are hard to access being enclosed within the phone itself. But iPhones usually also have two external LDI's. These are located in the headphone jack and dock area. To see them, you will need a torch. You should be able to see either a red or white dot. Red indicates water damage, whereas white will indicate no water damage.
If both dot's are white then your iPhone is perfect fine.
If your iPhone has two red positive dots then it's likely your phone has been affected by water damage. Although, there are two more LDI's on the inside which are hard to access as you will need to take your iPhone apart.
If your iPhone has one red dot and one white dot then it will also need to be diagnosed for water damage by the inside sensor too. Check out our You Tube video on how to diagnose water damage on an iPhone.