When there is water leaking from a light fixture in the ceiling, you either have a roof leak or plumbing leak that needs to be fixed as soon as possible. Both are definitely problems, but right now, you have an even more urgent one, because a leak near a light fixture is a serious electrical hazard.
As incongruous as it sounds, water collecting near a light fixture can start a fire. Count your blessings if it hasn't happened already, but there's no telling when it will, so you need to cut power to the fixture right away. It's good if the switch is off — and you should leave it that way — but just to be sure, you should also turn off the breaker that controls the light circuit until you can make repairs.
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Why the Water Leaking from the Ceiling is So Dangerous for Electrical Wiring
Pure water is an electrical insulator, but the water coming from your ceiling isn't pure. It's full of minerals, and those minerals turn pure water into an electrolyte, which is a fluid that conducts electricity. It can form a conducting bridge between the positive and negative fixture wires, causing a short circuit with arcing that can start a fire.
You might see water dripping from light bulbs or around fixtures because ceiling fixtures have plenty of holes through which water can seep. Both indicate that a pool of water has collected on the ceiling drywall. That water could easily be energized if you turn on the light, so you definitely don't want to do that. It isn't just the dangers of electricity that should concern you, however.
Dangers of Weakened Ceiling Drywall
It takes a while for water that collects on the ceiling to seep through the drywall and begin leaking from a light fixture. So, by the time you see the leak, the drywall has become weakened, and it could be on the verge of breaking. This is especially likely if the drywall is sagging.
Once the drywall breaks, the ceiling fixture will fall unless it's secured to a ceiling joist. If it does, and you haven't turned off the power, you'll have a mess of live wires on your floor, which is a nasty surprise if you're working in the kitchen or watching TV. Not to mention that the fixture could hit someone on the way down and injure them.
It takes time for things to get this bad, and during this time, mold has probably established itself in the drywall. The mold may have spread to other parts of the ceiling, requiring you to replace a large part of the ceiling.
What to Do
Whether you see water coming through a kitchen light or water coming out of a light switch, the most important thing to do is to turnoff the breaker controlling the circuit. If you can't access the breaker for some reason, call the power company and ask to have the power to your house shut off. It's important to do this immediately to prevent electrical accidents.
Once the power is off, get a ladder, disconnect the light fixture, take it down and screw caps onto the electrical wires. It may then be safe to turn the breaker back on. But to be sure, call an electrician to have the wires inspected because, as ServiceMaster DSI points out, they could be corroded. Once you get the all-clear, you'll need to find the leak and repair it, then repair the water damage to the ceiling. It's a better idea to install a brand new fixture than it is to reuse a fixture that is water damaged.