Agreed on the water heater - I can't see where anything feeds downstream from there. There isn't a separate breaker for the water heater, but I believe the electric heating element was added after-market (we aren't the original owners). I can see where the outlet just inside the house door feeds the water heater - it was probably easiest to do it that way.
I also agree with your assessment that the outlet just before the outdoor one might be the culprit. The problem is that I can't tell which outlet feeds that one.
Thanks for your help!
