How can you tell if a water heater is glass lined?

You can identify a glass-lined water heater by looking for specific labels or markings on the unit, often indicating "glass-lined" or "glass-coated." Additionally, if you can access the tank, check for a smooth, glossy surface inside, which is characteristic of glass lining. Another indicator can be the manufacturer's specifications or documentation, which usually detail the materials used in the tank's construction. If in doubt, consult the manufacturer's website or customer service for confirmation.