Energy Efficient Products: Gas Water Heaters - http://www1.eere.energy.gov/femp/procurement/eep_gas_waterheaters.html
Find Consumer information about gas water heaters, covering efficiency recommendations, cost effectiveness, technology options (such as demand-type and solar assisted water heaters), and other tips for buying and using water heaters. From the U.S. Department of Energy, Office of Energy Efficiency and Renewable Energy.
Water Heating - http://www.aceee.org/consumerguide/topwater.htm
Find a fact sheet on water heating, which "next to heating or cooling ... is typically the largest energy user in the home." The site discusses types of water heaters (storage, demand, heat pump, indirect, and solar), selection, efficiency, cost comparison, and upgrading your current water heater. From the online version of the Consumer Guide to Home Energy Savings.