DOMESTIC WATER TANK :-In household and commercial usage, most North American water heaters have traditionally been the tank type and in Southern Asia also the same. Also called storage water heaters, these consist of a cylindrical vessel or container that keeps water continuously hot and ready to use. Typical sizes for household use range from 75 to 400 liters (20 to 100 US gallons). These may use electricity, natural gas, propane, heating oil, solar, or other energy sources. Natural gas heaters are most popular in the US and most European countries, since the gas is often conveniently piped throughout cities and towns and currently is the cheapest to use