Hot water for domestic use is commonly provided by systems in which the water is heated by an independent boiler or a back boiler and stored in a cylinder or tank. Various materials have been used successfully for the tanks, cylinders and pipes, the commonest being copper and galvanized steel for tanks and cylinders, and copper, galvanized steel, lead and lead alloys for piping. Failures have been found to occur where copper pipes had been used in association with galvanized steel tanks.