Can I run the hot water heater with a generator

Problem with Rheem 40 GAL ELEC TALL Water Heater 6YR SC 82VH402

Can I run the hot water heater with a generator
Reverse polarity may not allow me to run the hot water heater with a generator



Yes.
Ordinary electric water heater can run on any voltage from any direction (excluding volt/amp ratings below what can heat element coil).

Voltages include single-phase, split phase, and 3-phase residential/commercial voltages with either 50 or 60 Hz.
http://waterheatertimer.org/How-to-wire-water-heater-for-120-Volt.html
http://waterheatertimer.org/How-to-wire-water-heater-thermostats.html#3-phase

Install line fuse.
30 amp fuse would be required to prevent wires from overheating, and eliminate fire hazard.

This information does NOT apply to energy-smart electric water heater with box on top of heater, or newer energy smart with electronics, or to hybrid water heaters, or heat pump water heaters with delicate electronic circuitry.

Why it works like this:
Ordinary electric water heater thermostats are mechanical bi-metal switches and respond to tank temperature, and are not operated by electricity. 
Ordinary generic elecrtic water heater thermostats switch electricity on-off using mechanical bi-metal switch.
Heat elements are simple coil of thermal wire that gets hot when voltage is applied.
The element will get hot when power is applied.