In accordance with the NC General Statues § 87-21, subsection (c) and 21 NCAC 50.0506 anyone who interrupts the water supply is required be properly licensed. When testing a backflow preventer one or both shut-off valves on the backflow preventer is required to be turned off during testing, therefore interrupting the water supply. North Carolina has a statewide licensing program for Plumbing, Utility, and Fire Protection Contractors. Part of the State licensing General Statue requirements is that these individuals are properly trained and certified to preform trouble shooting beyond the routine annual testing. By law, installation and repairs of backflow preventers can only be performed by a properly licensed person, carrying this requirement over to include testing allows the City of Durham to ensure quality work is carried over to each customer.