It might be a leak—start by looking for water around the tank and try to determine the source. One of the most common reasons for a water heater to leak is a loose drain valve. The drain valve will slowly leak water if it becomes loose. It is easy to stop a leaking drain valve by tightening it up with a wrench.
Then, what causes a hot water heater to burst?
When a water heater bursts, the cause is not always apparent. A malfunctioning thermostat could cause the heating element to overheat the water, making the volume inside of the tank too much for the seams to hold, or a fitting may have corroded, causing a major leak. Move quickly to disable a burst hot water heater.