Your iPhone will not take like a duck to water. Water exposure will not only kill your iPhone, it will void your one-year limited warranty. It is also not covered by an AppleCare Protection Plan. Finding yourself caught in a driving rain is not the only kind of water exposure that will turn off your iPhone. Any liquid spilled onto it will affect it. Your iPhone is also sensitive to humidity and sweat. Prolonged exposure to any kind of moisture can trigger the Liquid Contact Indicators located inside your headphone jack and your dock-connector opening at the bottom of the iPhone, which means that you have to pay to repair it.
Be mindful of your iPhone when it is raining. Your iPhone is not so fragile that it cannot be exposed to a drop of water without damage. Still, make sure you are savvy about answering or using your phone if you are unprotected. Keep a microfiber cloth with you if you are traveling when it is raining so that you can safely wipe your phone screen.
Never hold or use your iPhone during a workout, particularly when working out in a gym. The sweat from your hand and humidity within the gym could be enough to trigger your Liquid Contact Indicators and damage your iPhone. Use an iPod to listen to music while jogging. Sweat from your face could make its way down your headphone wires and into your iPhone's headphone jack, where one of the Liquid Contact Indicators are.
Leave your iPhone out of the bathroom if you are taking a shower. The steam and humidity that a hot shower can produce in a bathroom with the door closed could trigger your Liquid Contact Indicators and damage your iPhone.
Keep your iPhone in your pocket when eating or drinking. Avoid accidents by you, or by someone else, that could ruin your iPhone. A spilled drink on a different part of the table could reach your iPhone lying there before you can grab it and trigger the Liquid Contact Indicator in your dock-connector opening, which is particularly vulnerable with the iPhone prone.
Wrap your iPhone in a microfiber cloth if you are outside on a particularly humid day. High humidity and dew that accumulates on your iPhone could damage it. The cotton lining of your pocket could offer similar protection.
The Apple Store has changed its policy regarding out-of-warranty, water-damaged iPhones. Now, it will extract your SIM card and swap your damaged handset with a refurbished, working one for a fraction of what buying a new iPhone would cost.