Does water in the water heater drip pan mean my heater is bad?
My thermostat stopped working, my electric water heater got too hot, and water boiled out of the T&amp;P valve. I just had to replace the thermostat. Have it looked at by a plumber. 
So yes, this can be an intermittent thing. 

And yes, there could be a slow leak somewhere else. 

What type of WH is it? Gas, electric? Please add this answer to the bottom of your post.