While misty and rainy days make for ideal conditions for photographing subjects such as Kent Falls in Connecticut (above), there's occasionally the risk that moisture in the form of rain or high humidity can affect your camera. It's certainly frustrating when a body goes completely dead , but fortunately in many instances it will come back to life after the problem clears up, especially if the water contact was fairly light (as opposed to a full dunking or salt water, which are more likely to create big problems). The following are steps I've found helpful in dealing with these issues.
1. As soon as there's any evidence of moisture inside the camera (even if it is working correctly), try to keep it in the same position without turning it in different directions. This may keep water from reaching and affecting additional circuits and corners inside the body. As tempting as it may be to check, DO NOT turn on the power on until you're sure the camera is thoroughly dry, as this may cause an electronic short.
2. Though some suggest leaving external pieces attached, I immediately remove the lens, battery, and memory card, which protects them from being potentially damaged or compromised by the problem and also help the moisture dissipate from the body.
3. Now you have several options for the drying process. One possibility, especially if the water contact was light, is to place the camera in close proximity to an active light blub. The heat can slowly draw moisture out through openings such as switches and buttons. It should be close enough to feel the heat, but far enough away to not be in direct contact or feel hot to the touch.
Another simple and inexpensive option that has worked for many with wet cameras, lenses, and cell phones is to place the item in a sealed plastic bag with uncooked rice, which is excellent for absorbing moisture. You'll want to be careful that the grains and dust don't get into openings. Silica gel packs (which often come with electronic equipment and are definitely worth saving) are similarly effective.
4. Have patience. Problems may clear up in a matter of minutes or hours, or they may last as long as several weeks. Even if it looks like the problem has cleared up, it's best to continue the drying process for at least a couple days or longer. Continue to keep the camera/lens in a cool, dry environment. Try starting it with different combinations (i.e. lens or memory card attached, not attached, etc.) especially if there are symptoms such as beeps from the memory card door or unusual lens. Recently I had a Canon T1i out of service for an entire month, then suddenly come back to life.
5. Be aware that the camera may not function normally or consistently after a moisture incident - in other words be sure to take a bunch of test images and have a backup handy before heading out in the field again.