Every iPhone is equipped with at least one water damage indicator, known as a Liquid Contact Indicator. When your iPhone comes in contact with water or any other liquid, this indicator permanently changes from its normal white or silver color to red or pink. When you take your iPhone to Apple for repairs, the technician will inspect these indicators to determine whether the damage to your iPhone may have been caused by a liquid and the company may deny warranty coverage if the indicators have been triggered.
Headphone Jack Indicator
The main Liquid Contact Indicator in an iPhone is located at the bottom of the headphone jack. Examine your iPhone under a bright light, angling it so the light reaches the bottom of the headphone jack, to see whether or not this indicator has been triggered. You can also use a flashlight or a lighted magnifying glass to make the process easier.
Dock Connector Indicator
IPhones belonging to the third and newer generations have an additional Liquid Contact Indicator, located inside the dock connector at the bottom of the iPhone. This indicator is very small and quite hard to see with the naked eye. Use a lighted magnifying glass, directing the light to the bottom center of the housing for the dock connector, to check whether this indicator has been triggered.
Corrosion and Other Liquid Damage
If your iPhone's Liquid Contact Indicators have been triggered, thoroughly check your iPhone for signs of water damage. You should examine any metal parts, including the headphone jack, the mesh that protects the iPhone's speaker and microphone and the dock connector, and should also look for traces of liquid behind the iPhone's screen. If no signs of water damage are present, your iPhone may still be eligible for free repairs under a warranty or AppleCare protection plan.
Even if Apple agrees to repair your iPhone for free, all data on it will be lost unless you have backed up recently. Apple's repair process involves the erasing of all data. Furthermore, if the damage to your iPhone is so severe that it can't be repaired, you may receive a new or refurbished iPhone of the same model as your old one instead. If the data on your iPhone is important to you, back it up regularly using iTunes and take care not to damage your iPhone by getting it wet or in any other way.