Most people have used the services of a plumber at one time or another, perhaps, to unclog a drain or to install a new appliance. Plumbers, however, actually deal with a wide variety of pipe systems. Water lines are only one of these systems. For example, some plumbing systems bring in gas for stoves and furnaces, others supply air conditioning and heating and still others carry steam to run huge power plants. The plumber's work also involves the installation or repair of waste disposal systems, drainage systems and gas systems in residential, commercial and industrial buildings. Construction plumbers, working from blueprints, route new pipes and install bath and kitchen fixtures. Most plumbers work for a plumbing contractor and learn their trade through an apprenticeship program.