It is a system of pipes and fixtures installed in a building for the distribution and use of potable (drinkable) water and the removal of waterborne waste. Plumbing uses pipes, valves, plumbing fixtures, tanks, and other apparatuses to convey fluids. Heating and cooling (HVAC), waste removal, and potable water delivery are among the most common uses for plumbing. The water-carrying pipes and other materials used in a plumbing system must be strong, noncorrosive, and durable enough to equal or exceed the expected life of the building in which they are installed. Toilets, urinals, and lavatories usually are made of stable porcelain or vitreous china, although they sometimes are made of glazed cast iron, steel, or stainless steel. Ordinary water pipes usually are made of steel, copper, brass, plastic, or other nontoxic material; and the most common materials for sewage pipes are cast iron, steel, copper, and asbestos cement.