Master plumbers install and repair various commercial and residential plumbing systems. The title of master plumber is specially given to those who successfully pass the licensing exam issued by the state. Common residential jobs for master plumbers include installing water heaters, repairing faucets and toilets, sewer machine service, gas line service work, and water service line installation. Some master plumbers work in the public sector in wastewater treatment plants or other municipal water systems. Some master plumbers choose a specialty such as pipe installation or pressurized water systems. Working hours can range from full-time on a construction site to whatever works for the client's schedule.