There shall be a backflow prevention device installed at every connection to a public water system if the facility connected may pose a hazard to the quality of water supplied by the public water system as determined by the department. Where applicable, the facility receiving water from a public water supply shall be responsible for having such drinking water distribution system protective backflow prevention devices inspected and tested by individuals certified by a third party who has been approved by the department to conduct backflow device inspection and testing certification. The facility shall also have backflow devices installed, maintained, repaired, and replaced by individuals qualified by either a plumbers license or by certification by the department under N.H. Rev. Stat. § 332-E:3, III proving competency in distribution system operation. The activities to be conducted by qualified individuals shall be specifically limited to the inspection and testing, maintenance, repair or replacement, and installation of the water meters, meter horns, backflow preventers, and assembly devices directly adjacent to and required as part of the protection for the drinking water distribution system. Testing of drinking water distribution system protective backflow prevention devices, where applicable, shall occur after installation or repair to ensure that new and repaired devices are working properly. There shall be a backflow prevention device installed at every connection to a public water system if the facility connected may pose a hazard to the quality of water supplied by the public water system as determined by the department of environmental services. The facility receiving water from a public water supply shall be responsible for having such backflow prevention devices installed, serviced, and tested by individuals qualified by license or certification to perform these activities. Testing of backflow devices shall occur twice annually unless the public water supplier determines the facility poses a low hazard, in which case testing shall be performed on an annual basis. The facility receiving water from a public water supplier is responsible for ensuring that the backflow prevention device is working properly to prevent backflow into the public water system. Testing shall also occur twice annually for any high hazard devices and facilities. When the public water supplier determines that the facility poses a low hazard, testing shall occur annually. A residential property containing a non-testable device shall not be considered a hazard facility and shall not require annual testing. A residential property may be considered a high hazard facility if it has an irrigation system, private well connection, or other feature that may cause a public health risk. If an outside irrigation system is the sole reason a residential property is considered a hazard to the public water supply distribution system, such irrigation system shall be tested annually during the period when the irrigation system is operated. The facility receiving water from a public water supplier is responsible for ensuring that the backflow prevention device is working properly to prevent backflow into the public water system.