Many homeowners who are extra vigilant turn off the water and the power to their water heater before they leave, to avoid any risks of floods or fires. But that can spell disaster if you turn things back on in the wrong order; the tank needs to fill with water before you switch on the heater. John Palanca of Design Tech, a general contractor in New York City, says he's burned out the element in his water heater more than once at his vacation home when visitors turn it on with no water in it. "I keep extra elements around just in case."