Few people realize the important role water plays in our daily energy use, or the energy required to heat, treat, and supply water. Powering one 60-watt bulb for 12 hours a day over the course of a year can require 3,000 to 6,000 gallons of water — enough to fill a large tanker truck. Meanwhile, the electricity used for water treatment can be as much as one-third of a city’s energy bill.