Electric Water Heater

Can anyone tell me where in the IRC it states that an electric water heater must be elevated 18" in a garage?

It doesn’t. “Ignition source” must be elevated 18".

The ignition source must be 18 inches above the floor. When you read the definition for ignition source it becomes clear that the contacts in the electric water heater are a source of ignition.

Per IRC R202

For my home installation, I needed to raise the unit about 8 inches to get the ignition source above 18 inches.

For gas appliances

Water heater specific, regardless of fuel

Thank you, would you have the reference?

That answered my question, thank you for your help.