I noticed my water heater drips water, but only when the burner is firing and not every time. Im guessing that the tank is failing. How long do I have before my garage is full of water?

Depending were you live it could be condensation when the cold water meets the hot flame it will drip condensation

I live in las vegas, not much condensation... but it has been humid today. I only looked at it closely because we ran out of hot water sooner than usual today... 1 shower, 1 load of clothes. Thanks for the tip, I'll keep and eye on it