http://chamblissplumbing.com/choose-the-right-water-heaters-for-your-home/
In homes and commercial areas, storage tank heaters are used. Gas, solar and electric power sources are available. One tank can hold a few or a hundred gallons of water. Tank heaters use energy at a slowed pace so that water is retained for longer. Some San Antonio consumers use solar heaters with panels and collectors that are installed on house exteriors.