For conveinence of installation they are electrically heated. But, that would be neat, that as you take a hot shower the hot water heats up the towel also (double duty). But, with electrically heated ones you can spend all day in tub and still get a nice warm towel

You can have either only electric or only water heated. In the summer when you turn your heating off the water heating the towels wont work. The electrical ones work all year roundI have found an adapter that allows me to have a water heated towel rack in the winter when the heating is on, and switch to electric in the summer.