Find the valve on the cold water pipe going into the top of the tank and turn it clockwise until it stops. This stops more water from feeding the leak.
For an electric unit, flip the breaker. For a gas unit, turn the dial on the front to 'off.' Never leave a leaking heater running.
Hook a garden hose to the drain valve at the bottom and run it to a lower spot outside or to a floor drain. This takes pressure off the tank and slows the mess.
Boxes, laundry, and stored items in the garage or closet soak up water fast. Get them up and out of the puddle.
Most tank water heaters sit in a garage or a hall closet here in Monterey. When you see water at the base, the first question is where it's really coming from. A drip from the top fittings or the temperature relief valve is often a simple fix. Water spreading out from under the tank itself is different. That's the steel tank rusting through from the inside, and once it goes, there's no repair for it.
The salt air off the bay is hard on metal. Tanks in New Monterey, Cannery Row, and Pacific Grove tend to corrode a little faster than you'd expect, and the anode rod inside wears out over the years. When our plumber comes out, they check the drain valve, the relief valve, the fittings, and the base of the tank to tell you exactly what failed. If it's just a valve, you keep your heater. If the tank is done, they'll size a new one for your household and haul the old one away.
Treat this as urgent if the water is spreading toward drywall, electrical panels, or a finished floor. A slow tank leak turns into a burst tank, and a full tank dumps forty or fifty gallons at once. We're at your door in about 45 minutes across the Peninsula, so you don't have to babysit a puddle all day.
Describe what you're seeing to a real Monterey plumber: call (210) 555-0134 or send the form. Free, no obligation.