Look for the cold water line coming into the top of the tank. There's a valve there. Turn it clockwise until it stops. If the leak is already pooling, do this first.
If it's gas, turn the dial on the heater itself to the pilot or off position. If it's electric, flip the breaker for the water heater at your panel. You want to stop heating while water is escaping.
Turn on a sink or tub in the house to relieve pressure inside the tank. Let it run until nothing comes out. This keeps water from forcing its way out the leak.
Move items away from under the tank. You're buying time before a plumber arrives, not stopping the leak entirely.
A water heater tank has a steel shell and a glass lining inside. Both wear down. The lining cracks first, and water touches the steel underneath. Rust starts. Over years, a small hole forms. Scotts Valley's water has minerals in it, especially in the foothills and mountain communities like Boulder Creek and Ben Lomond. Those minerals settle as sediment at the bottom of the tank and eat away at it faster. By the time you see water pooling under the heater, the tank is usually past fixing.
A plumber will check where the leak is coming from. Sometimes it's the drain valve at the very bottom, which is cheaper to replace. More often it's the tank wall itself. If the tank is leaking, you need a new heater. This is not a repair that lasts. Waiting a few days usually means more damage to your floor or the area around the heater.
Homes in Scotts Valley, Los Gatos, and Capitola tend to run water heaters hard. You're in an area where supply and demand shift seasonally, and the mineral content in the water means tanks need attention. If your heater is more than ten years old and you see pooling water, replacement is almost certainly coming. We can be at your door in about 45 minutes from the time you call, inspect the tank, and tell you the exact next step before any work starts.
Describe what you're seeing to a real Scotts Valley plumber: call (831) 555-0179 or send the form. Free, no obligation.