What many people (even news anchors on well-respected TV news channels!) call a water heater.
You
don't want to heat
water that's already hot for Pete sakes!! It's proper to call it a 'water heater' or you can even call it a 'hot water
tank' -- but never a 'hot water heater'.
{Latoya}: Gary, I think the hot water heater is busted; I can't get any hot
water out of this faucet to do the dishes!
{Gary}: Latoya, we
don't have a 'hot water heater' -- we might have a hot water cooler, a water heater, or a hot water
tank, but no hot water heater! Which of those do you want me to check?