City of Columbus

Standards for Non-residential Properties

Requirements are based on the type of water service line.  Additional situations related to your plumbing or site use may carry additional requirements.  These are described immediately below.  More than one situation may apply to your site. Descriptions of the types of devices and applicable standard detail drawings are further down the page.

• Domestic water service lines
  An RP type backflow preventer or an air gap must be provided at the outlet to the water meter. If the meter is in an underground vault outside the building the RP must be installed in an above ground heated enclosure immediately after the meter. The size of the device must match the size of the meter. Installation must follow Division of Water Standard Detail Drawings unless otherwise approved.      
• Fire-only Water service lines
  Either an RPDA type backflow preventer or an air gap with a water meter must be provided at the end of the service line. The size of an RPDA must match the size of the service line. The backflow preventer may be installed inside where the water line enters the building, as long as the length of the service line from the property line to the backflow preventer does not exceed 150’. Otherwise the RPDA must be installed near the property line in an above ground heated enclosure. Installation must follow Division of Water Standard Detail Drawings unless otherwise approved. If the fire suppression system uses water only, in some cases a DCDA type backflow preventer may be used in lieu of the RPDA.  If installed outside the building DCDAs may be located in a vault or an above ground heated enclosure
• Properties with toxic or hazardous chemicals used with water 
  Piping for processes using toxic chemicals and water cannot be interconnected in any way that could provide a path for the toxic chemical to get into the public water system. If water is needed for use with the chemical it must be provided through an air gap at the point of use. An RP is also needed at the meter.
• Properties with a second water system on site 
  Wells, ponds for fire suppression systems, etc. cannot be interconnected in any way that could provide a path for the water from the auxiliary system to get into the public water system. If water from an auxiliary system is used to supplement a process or equipment using City of Columbus water, or vice versa, the water from the City of Columbus must be fed through an air gap.
• Booster pumps not for fire protection 
  A low pressure cutoff switch must be provided.
• Booster pumps for fire protection 

  Installed on or after August 8, 2008:
  Either a discharge throttling valve or a variable speed controller must be provided.

  Installed before August 8, 2008 without a low pressure cutoff switch:
  Either a discharge throttling valve or a variable speed controller must be provided.

  Installed before August 8, 2008 with a low pressure cutoff switch:
  No modification is required

Types of Backflow Prevention Methods

• Air Gap
  An Air Gap provides the best protection. This is quite simply a vertical opening/gap between the outlet of the pipe or faucet supplying water and the potential source of contamination. The gap, measured from the bottom of the fill outlet to the overflow elevation of the tank/basin, must be at least twice the height of the fill pipe diameter, and no less than 1”. For instance, a 2” diameter fill pipe requires a 4” air gap.
• Reduced Pressure (RP) assembly
  A Reduced Pressure Assembly, also known as a  Reduced Pressure Zone (RPZ) assembly is the next best thing to an air gap. RPs must meet ASSE Standard 1013 and may not be installed in a pit/vault.
• Reduced Pressure Detector Assembly (RPDA)
  A Reduced Pressure Detector Assembly is an RP type device that also contains a special type of meter for fire-only water service lines. RPDAs must meet ASSE Standard 1047 and may not be installed in a pit/vault.
• Double Check (DC) assembly
  A Double Check assembly is effective in certain uses, but less effective than an RP. DCs must meet ASSE Standard 1015.
• Double Check Detector Assembly (DCDA)
  A Double Check Detector Assembly is a DC type device that also contains a special type of meter for fire-only water service lines. DCDAs must meet ASSE Standard 1048.

Types of Low Pressure Sustaining Devices/Methods

• Cutoff Switch
  Shuts off the pump if the pressure on the suction side of the pump drops to 10 psi or less.
• Discharge Throttling Valve
  Automatically throttles (reduces) the flow of the pump by closing a valve on the discharge side of the pump to maintain the pressure on the suction side to 10 psi or greater.
• Variable Speed Controller
  Automatically reduces the flow of the pump by slowing the pump speed to maintain the pressure on the suction side to 10 psi or greater.

Standard Detail Drawings - Domestic Water Service

Domestic Water Service Lines (including combined domestic/fire water service lines), listed by backflow preventer type and location.

• Meter inside, Reduced Pressure Assembly (RP) at meter

  5/8" - 1" Meter/Service Size
  L-9002B and L-9002E

  1 1/2" Meter/Service Size
  L-9002B and L-9002C

  2" Meter/Service Size and Larger
  L-9002B and L-9002F

• Meter in vault, RP in above grade heated enclosure
  L-9002B and L-9002G

Standard Detail Drawings - Fire-only Water Service

Fire-only Water Service Lines, listed by backflow preventer type and location.

• RPDA in building (includes meter)
  L-9002B and L-6317C
• RPDA outside, above grade, in heated enclosure (includes meter)
  L-9002B and L-9002G
• DCDA in building, includes meter
  L-9002B and L-6317C
• DCDA required outside in vault, includes meter
  L-9002B and L-6317A and L-6317B