Home improvement stores, such as Home Depot and Lowe's, sell a variety of water tanks, as do department stores, such as Kmart. Water heaters are also available for online purchase through retailers, such as Amazon.
Home improvement retailers, such as Home Depot and Lowe's, offer the widest variety of in stock hot water tanks in their brick and mortar stores. Their sales staff can usually help consumers choose a hot water heater. Such stores can order other models if they do not have a specified tank in stock.
Kmart is another retailer where consumers can buy hot water heaters both in store and online. The Kmart website offers their models classified according to categories, such as electric, natural gas, brand and top sellers. Many of the water tanks also come with user reviews. Kmart also features sale pricing on many models.
Amazon is a strictly online retailer that also has user reviews and sale pricing. Amazon sells merchandise from stores, its own stock and from independent sellers. Used water tanks are also available on Amazon and on eBay.
For consumers who know which brand they want, that brand's website is a good place to start. For instance, the Kenmore website offers 29 models of hot water tanks ranging in price from $275 to over $750 as of 2015.