I use an absorbent towel if practical. These towels can be draped over the camera and lens and will absorb virtually 100% of falling rain. When they are too wet, you just wring it out and put it back over your camera. The key to this approach is you never have drips or collected water on your camera, over seals, etc. If you are on a tripod it's quite convenient.
View attachment 89073
If you are mobile, there are a wide range of covers. The top of the line is the Think Tank Hydrophobia. This cover actually attaches to your camera and covers the lens. It's good for ongoing torrential rain - but still won't help with submerging your gear.
I normally will have had enough rain before my camera reaches that point. My approach is a Vortex Storm Jacket. I also have a couple of disposable covers. The Storm Jacket is in a small pouch clipped to my camera bag at all times. I've used it for rain, snow, and blowing sand or dust. It's not a perfect solution, but gives you 90% of the protection you would get with the Hydrophobia while being convenient and inexpensive.
It's important to blot any water on your camera or controls. Use a cloth that absorbs the moisture. Don't wipe moisture across buttons or covers where it can be forced into the camera.
Fresh water is much less of a problem than salt or alkaline water. Cameras and lenses can survive fresh water - especially if you remove the power and let it dry completely after getting wet. I use a heating pad or a warm electric appliance to dry cameras and lenses after extensive moisture or water exposure.
