Power goes off fairly frequently in FL. A common but dangerous thing to do is turn off the main breakers, make a suicide power cord, and plug into the dryer outlet to back feed the house. This way the water heater, and both sides of the panel can be powered.
I would recommend disconnecting the power cable going to the water heater, and putting in an outlet on the wall, and a 220V plug on the tank. This would make it easy to unplug the W/H from the house, and plug it into the generator via an extension cord (please don't run a generator in the garage).
Or... put in a transfer switch and be done with it.
I took a different path. Hurricanes are common here. In 2004, we lost power for 18 days. Almost impossible to feed a conventional generator for that period of time since gas stations were closed - they didn't have power either. I bought a Yamaha EF2400iS inverter type, which only uses 1.6 gallons in 8 hours (1/4 load) vs. 1.0 to 1.5 gallons per hour with a conventional generator.
I can't run my W/H, but I can run a 5000 BTU A/C window shaker, TV, lights, fan, computer, etc. I keep our 25' travel trailer next to our house, and it has a shower and fridge that both use propane as the energy source.