Although the pipe trades are sometimes considered a single trade, workers generally specialize in one of three trades. Plumbers repair, install, or alter the water, waste disposal, drainage, and gas systems in homes and commercial and industrial buildings. They install plumbing fixtures: bathtubs, toilets, sinks, showers, and appliances such as dishwashers and water heaters. Pipefitters repair and install both high and low-pressure pipe systems that are used in manufacturing, in the generation of electricity, and in heating and cooling buildings. They also install automatic controls that are used to regulate these systems. Steamfitters install pipe systems that move liquids or gases under high pressure and provide refrigeration installation and service. Sprinkler fitters install and service fire protection systems including fire standpipes, sprinklerheads, and fire pumps.