Turn off the power to the water heater at the breaker panel if it is electric
Turn the gas control knob to Off if it is gas
Close the cold water supply valve to the heater
Turn off the water heater switch if one is installed
For gas heaters, turn the thermostat to the lowest setting before switching Off
If needed, shut off the gas supply valve to the heater
Verify the heater is off by checking that indicator lights or burners are no longer on