If you suspect you've got a leaking hot water system, call a licensed plumber as soon as you can. If you're sure it's not a leak and you have a gas or gas-boosted hot water system, check the gas supply - your pilot light might be out which means you'll have to look at the manual to see how to relight it.
If you've got electric hot water the circuit breaker for your water heater will generally only trip if there's a major problem with your hot water unit - it's best to call an electrician if this is the case.