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This page is intended to be a single source where individuals, water professionals and plumbers can exchange and share questions, thoughts and ideas concerning cross-connection control and backflow prevention.

Illinois Environmental Protection Agency Rules and Regulations Title 35 provides the guidelines that all State of Illinois water supplies must follow to ensure a safe and adequate supply of potable water for all residents and businesses in Illinois.

The Illinois Plumbing Code dictates the requirements of backflow devices. Each of the parts of the plumbing code relating to backflow devices are listed below.


We hope that you will find answers here to your common backflow questions. If you would like to ask additional questions, email or post your question on our forum.

We hope that you will find answers here to your common backflow questions. If you would like to ask additional questions, email or post your question on our forum.

Frequently Asked Questions

  • Why is it important for the water customer and water suppliers to prevent Backflow?

Under certain circumstances of unequal pressure, a non-drinkable substance could either be pulled or pushed into a drinking water supply. This is called backflow.

Backflow can reverse the flow of water or other substances into the public or private water system, resulting in chemicals or contaminants getting into the drinking water. In other words, due to changes in pressure, the water can flow in the opposite direction from what is intended. This is why the installation, inspection and proper maintenance of Cross-Connection Control Devices is imperative to the safety of your drinking water.

  • What are some common backflow devices that I would find to in my home to prevent backflow?

Hose bibb vacuum breaker

Atmospheric vacuum breaker (dishwashers, soap dispensers, etc)

Reduced pressure (RP also called RPZ) principle assemblies

Air Gap (AG)



Used mainly on tanks and sinks, is a gap between the outlet and the basin. Requirements: The gap needs to be a minimum 2 times the supply pipe diameter.

Hose Bibb Vacuum Breaker (HBVB)

A simple device used to prevent backflow installed on an outdoor faucet.


There are two types of backflow: back-pressure and back-siphonage.

  • Back-pressure is when the water supply is connected to a device that creates pressure, such as a boiler, pressure washer, etc. The pressure created can be greater than the water supply, thereby creating backflow.

  • Back-siphonage is when there is a loss of pressure in the water supply. This will cause the water in your facility to flow backwards back into the water supply and/or into other plumbing connections within your facility. This situation can occur when a fire hydrant is opened, when there is a water main break, etc.

Atmospheric Vacuum Breaker (AVB)

An AVB is a non-testable mechanical backflow preventer with a gravity opening poppet air opening, designed to admit atmosphere into the downstream sides of the unit under a no flow condition to prevent back siphonage. It must be installed 6-inches above highest downstream water discharge. There shall be no valves or reduction of pipe size on its downstream side.

(Note: This device is installed on certain equipment that uses potable water by the manufacturer or contracted installer. Examples of this equipment are dishwashers, soap dispensers, faucets and deep sinks, etc.). The type of backflow protection required is based on the degree of hazard that the property represents to the potable water supply.

Reduced Pressure (RP) Principle Assemblies

A reduced pressure principle assembly is a mechanical valve assembly that consists of two internally loaded independently operating check valves and a mechanically independent, hydraulically dependent relief valve located between the check valves.

It is used for services that have either health hazards or non-health hazards and under conditions of back pressure or backsiphonage. It provides the highest level of protection among the mechanical backflow prevention devices.

Can you give some examples of cross connections?

  • A hose is submerged in polluted or contaminated water
  • A secondary source of irrigation water (from a well or pond) is pumped into an irrigation system that is directly connected to the potable water supply system
  • A heating boiler with treatment chemical added to prevent internal corrosion is connected directly to the water supply for make-up water
  • An underground lawn sprinkler system is directly connected to the water supply system
  • A fountain or swimming pool has a direct connection with the water system for filling

In all of these examples, a sudden drop in water pressure could draw contaminants – chemicals, fertilizer, soapy water or even bacteria -- back into your pipes and your drinking water supply. Any of these contaminants could be hazardous to your health if ingested.

The best way to prevent this potential contamination is to eliminate the cross connection. This could mean simply making sure that you never leave a hose submerged in a tub of water or that you never apply fertilizer to your lawn with a hose-aspirator device. In some cases (such as the lawn sprinkling system example noted above) the cross connection cannot be eliminated and the only means of protection is by installation of an approved backflow prevention device.

How do I know if I need a backflow prevention assembly?

Your local plumbing inspector or local licensed plumbing contractor can determine if you have an actual or potential cross-connection and the type of backflow prevention that may be required.


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Backflow best practices and related documents.
Item Name Posted By Date Posted
Chicago CCCDI Documentation New Data Entry Format PDF (977.14 KB)  more ] Administration 3/2/2016
PSA - Backflow WAV (2.16 MB)  more ] Administration 6/25/2015
APBA 2013 Residential Backflow Hazards PDF (833.59 KB)  more ] Administration 11/4/2014
Official Version of the Plumbing Code 7-7-14 PDF (3.31 MB)  more ] Administration 8/25/2014
Backflow Bulletin 1 - Fire PDF (395.18 KB) Administration 11/14/2011
Backflow Bulletin 2 - Boilers PDF (141.66 KB) Administration 6/11/2012
Backflow Bulletin #3 PDF (373.02 KB) Administration 1/23/2017
Backflow Bulletin #3.1 PDF (416.45 KB) Administration 1/23/2017
Backflow Bulletin 4 - Restaurants PDF (124.68 KB) Administration 8/7/2012
Backflow Bulletin Binder: 1 - 4 PDF (630.29 KB) Administration 8/7/2012
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