A little splash won't kill a device, but if your cellphone is caught in the rain, soaked by a spill, or dropped in the toilet, water can seep inside the case and wreak havoc.
Unfortunately, warranties almost never cover water damage. Many gadgets come with liquid-sensitive stickers that permanently change color when exposed to water. One drop is enough to dissolve the warranty forever. So should your cellphone start to drown, it's up to you to play lifeguard.
First step: Do not turn on the phone to see if it's all right. Waking it up can short out the circuits. Instead, remove the battery, wipe away as much water as possible, then toss the device into a bowl of uncooked rice. Dry rice is a natural desiccant. Covering your phone and battery in the grains overnight should wick away any moisture. Another option: those silica bags that come with coats and shoes.
Can't find either? A vacuum can suck out some moisture, but never use a hair dryer. The hot air will cook your device.