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Johnston County Inspection Hours Mon - Fri 8:00 am - 5:00 pm  Mon - Fri 8:00 am - 5:00 pm  
Johnston County Inspection Phone 919-989-5060 919-989-5060

Johnston County Inspection Address 309 E. Market Street - Smithfield NC 27577 309 E. Market Street - Smithfield NC 27577  309 E. Market Street
Smithfield NC 27577 

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Commercial, Agricultural, Industrial and Institutional Water Connections

Domestic Water

The water distribution system shall be sized in accordance with sound engineering practice. When required by the plumbing official, a licensed Mechanical, Civil, or Environmental Engineer shall size the water distribution system.

All commercial, agricultural, industrial, and institutional domestic water services require the following components:

  1. Cutoff Valve – A cut-off valve will be the first fitting out of the meter box at the street

Cut-off Valve

  1. Reduced Pressure Zone (RPZ) – An RPZ is a backflow prevention device consisting of two independent check valves, plumbed in series, with a pressure monitored chamber between. The RPZ must have testable ports and shall be sized based on the water distribution


  1. Pressure Reducing Valve - A pressure reducing valve must be installed at a location between the first cut-off valve at the mater and the first plumbing fixture in an accessible location.

  2. Thermal Expansion Tank – A thermal expansion tank or valve is required to absorb excessive pressure due to thermal expansion.



The RPZ may be installed in one of three approved installation arrangements, as listed below:

  1. Above Ground Hotbox - The insulated approved hotbox must be large enough to accommodate all piping to be installed. The property owner is responsible for providing power to the hotbox
  2. Below Ground Vault - Vault must have a positive drain or sump pump and be approved by the Plumbing Inspector. In addition, the Department of Utilities must approve the vault and proposed drainage method if housed in the same vault as the water meter. There shall be 12 inches minimum clearance from the vault walls and floor. The property owner is responsible for providing power for the sump pump.
  3. Inside Building – The RPZ and pressure reducing valve can be inside the building, at an appropriate location deemed acceptable by the Plumbing When the RPZ is inside the building, a double check valve assembly must be installed with the cut-off valve at the road right-of-way.

A number of RPZ backflow prevention assemblies are available for different applications. However, many of these assemblies do not have a pressure reducing valve included in the assembly. Johnston County requires a pressure reducing valve to be installed as a part of the plumbing distribution system to protect the system from pressures exceeding 80 psi.


The RPZ shall be tested by a certified professional within five working days of installation and once every two years thereafter.


After final inspection is made, contact Johnston County Public Utilities to have the meter installed. An inspection notice will be left at the job side by the Plumbing Inspector indicating approval or corrective measures required.

Fire and Sprinkler Lines

The testable backflow assembly and cut-off valve can be located in the riser room, as long as the water line for the fire protection system from the public water line connection to the riser room of the building does not exceed a maximum distance of 300 feet. Sprinkler system monitoring and alarms are required to meet Chapter 9 of the Fire Prevention Code. Fire protection lines exceeding 300 feet must have testable RPZ assemblies located in close proximity of the water connection at the street right-of-way or public water main.

In either case, a gate valve must be installed at the street right-of-way or public water main separating the public line from the private fire line. All sprinkler lines require a testable backflow assembly. Testable double check valve shall be installed, as a minimum. Fire protection lines with booster pump facilities, chemical injection, or other hazardous lines as deemed by Johnston County shall require a testable RPZ for backflow prevention.












Page last updated: May 12, 2022

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