Plumbing may be defined as the practice, materials and fixtures used in the installation, maintenance and alteration of all piping, fixtures, appliances and appurtenances in connection with sanitary and storm drainage facilities, the venting system, and public and private water supply systems. Plumbing does not include the trade of drilling water wells, installing water-softening equipment, or the business of manufacturing or selling plumbing fixtures, appliances, equipment or hardware. A plumbing system consists of three separate parts: an adequate potable water supply system; a safe, adequate drainage system; and ample fixtures and equipment. (read full article on InterNACHI)