Life-cycle costs, which take into account both the initial costs and operating costs of different water heaters, provide a much more accurate representation of the true costs of the water heater than the purchase price alone. Life-cycle costs for the most common types of water heaters under typical operating conditions are shown in the table here. When both purchase and operating costs are taken into account, one of the least expensive systems to buy (conventional electric storage) is one of the most costly to operate over a 13-year period. An electric heat pump water heater, though expensive to purchase, has a much lower cost over the long term. A solar water heating system, which costs the most to buy, has the lowest yearly operating cost among electric systems.