Turn off the water heater power or gas supply
Shut off the cold water supply valve
Turn off the breaker for an electric water heater
Let the water cool if possible
Attach a garden hose to the drain valve
Run the hose to a safe drain location
Open a hot water faucet in the house
Open the drain valve on the water heater
Open the pressure relief valve if needed
Drain the tank completely
Close the drain valve
Remove the hose
Close the hot water faucet
Turn the cold water supply back on briefly to flush sediment if desired
Close the hot water faucet again
Refill the tank fully before restoring power or gas
Turn the power or gas back on only after the tank is full