this may help-
Liquid contact indicators
All iPhones (and many other devices by Apple) have a small disc at the bottom of the headphone jack that changes from white to red on contact with water; iPhone 3G and later models also have a similar indicator at the bottom of the dock connector,Because Apple warranties do not cover water damage, employees examine the indicators before approving warranty repair or replacement.
The iPhone's indicators are more exposed than those in some mobile phones from other manufacturers, which carry them in a more protected location, such as beneath the battery behind a battery cover. The iPhone's can be triggered during routine use, by an owner's sweat,steam in a bathroom, and other light environmental moisture.Criticism led Apple to change its water damage policy for iPhones and similar products, allowing customers to request further internal inspection of the phone to verify if internal liquid damage sensors were triggered.