Backflow Prevention

Air Gap (AG)

A method of preventing backflow by using the unobstructed vertical distance between the lowest opening of any pipe or faucet supplying potable water and the flood-level rim of any receiving vessel, such as a tank, pool or fixture.  An "approved" air gap separation must be at least twice the effective opening (the inside diameter) of the supply line piping, but never less than one inch.

Air Gap

Air Gap with 1 sidewall

 Air Gap with multiple sidewalls

Reduced Pressure Backflow Assembly (RPBA)

An approved assembly providing protection against both backpressure and backpressure, as well as health and non-health hazards. A reduced-pressure principle backflow prevention assembly consists of two independently acting internally loaded check valves, a differential pressure-relief valve, four properly located test cocks, and two isolation valves.

The reduced pressure principle backflow prevention assembly is referred to as the RP, RPPZ, RPZ as well as other acronyms. The RP is the best mechanical backflow preventer available today. It is considered as proper protection for high- or low-hazard applications, backpressure or backsiphonage backflow and containment or isolation protection.

The name of this assembly is derived from a zone of reduced pressure needed for the operation of the relief or vent valve. This device is an assembly of two internally loaded, specially designed and independently operating check valves that have a relief valve installed between the primary valves, specifically designed to maintain a zone of relative differential pressure between the two check valves unless one or both of the check valves are fouled.

Reduced Pressure Backflow Assembly (RPBA)

Reduced Pressure Backflow Assembly (RPBA) Outside Enclosure

Reduced Pressure Backflow Assembly (RPBA) PNW-AWWA Vault Standard

Reduced Pressure Detector Assembly (RPDA)

This standard applies to the two types of assemblies, identified as:

(a) Reduced Pressure Detector Assembly (RPDA); and

(b) Reduced Pressure Detector Assembly Type II (RPDA-II).

The RPDA and RPDA-II assemblies consist of two (2) independently acting check valves, internally force loaded to a normally closed position, and separated by an intermediate chamber (or zone) in which there is a hydraulically operated relief means for venting to atmosphere, internally force loaded to a normally open position. These assemblies are designed to operate under continuous pressure conditions. The assembly includes two (2) properly located, tightly closing shut-off valves and properly located test cocks. The assemblies also include a bypass line which provides a visual or audible indication of system leakage or unauthorized use of water. 

Reduced Pressure Detector Assembly (RPDA)

Double Check Valve Backflow Assembly (DCVA)

An approved assembly designed to protect against both backsiphonage and backpressure that are subject to low health hazard conditions.  The Double Check Valve Assembly (DCVA) is an approved backflow assembly consisting of two single check valves assembled within one body and furnished with four test cocks and two shut-off valves. Double checks are commonly used to protect against low to medium hazard installations such as food processing equipment or lawn sprinkler systems.

Double Check Valve Assembly (Irrigation Installation)

Double Check Valve Backflow Assembly (DCVA)

Double Check Detector Assembly (DCDA)

An approved assembly designed to protect against both backsiphonage and backpressure that are subject to low health hazard conditions. This standard applies to Double Check Detector Assembly (DCDA) and Double Check Detector Assembly Type II (DCDA-II). The DCDA and DCDA-II assemblies consist of two (2) independently acting check valves, internally force loaded to a normally closed position. These assemblies are designed to operate under continuous pressure conditions. The assembly shall include two (2) properly located, tightly closing shut-off valves and properly located test cocks. The assemblies also include a bypass line which provides a visual or audible indication of system leakage or unauthorized use of water. This standard also applies to Manifold Double Check Detector Assemblies consisting of two (2) or more complete DCDA or DCDA-II assemblies in parallel.

Double Check Detector Assembly (DCDA)

 Pressure Vacuum Breaker (PVB)

An approved assembly installed in water supply lines to prevent the entrance of non-potable material into the potable water supply by backsiphonage (only) and are intended for use in both high and low hazard applications. 

Pressure Vacuum Breaker (PVB)

Spill Resistant Vacuum Breaker (SVB)

An approved assembly designed to protect against backsiphonage only in low and high health hazard conditions.   The SVB is similar to the PVB, however it is designed to be spill-resistant for indoor use. Like the PVB, the SVB is designed to protect against backsiphonage and is not to be subjected to backpressure. Typically, the SVB is installed on chemical-soap dispensers, x-ray supply lines or tank fills.

Spill Resistant Vacuum Breaker (SVB)

Clearance & Accessibility Requirements(PDF, 195KB)

Cross-Connection Control Responsibilities(PDF, 116KB)

Cross-Connection Control Terminology(PDF, 233KB)

Lawn & Irrigation Systems & Backflow Prevention(PDF, 183KB)

What is Thermal Expansion?(PDF, 116KB)

Residential Fire Systems(PDF, 156KB)

How Cross-Connections Create Health Hazards(PDF, 178KB)

Protect Your Drinking Water Tips(PDF, 160KB)

A cross-connection is an actual or potential pathway connecting a source of pollution or contamination with a drinking water supply.  

Backflow is the undesirable reversal of flow of a liquid, gas, or other substance in a potable water system as a result of a cross connection. To prevent backflow from occurring, a backflow preventer—either an assembly or device must be installed.

Backflow may occur due to high pressure on the customer side, or low pressure in the water system. Backflow through a cross-connection can contaminate the drinking water in a building, on a block, or throughout an entire public drinking water system. 

The reverse flow of water due to negative pressure.

Backsiphonage is created when there is a sudden drop in water pressure in water mains due to water main breaks, nearby firefighting efforts or high usage.  A reversal of normal flow due to downstream pressure being greater than supply pressure.

A reversal of normal flow due to downstream pressure being greater than supply pressure.

Heating systems, elevated tanks, and pressure producing systems can create pressures in the customer's’ plumbing which exceeds the supply pressure.  An example would be a commercial boiler system operating at 100-150 lbs. of pressure. If the city’s water pressure is around 40-60 lbs. of pressure and water flows in the direction of least resistance, a back pressure would be created.  The contaminated boiler water could flow into the drinking water supply.

An approved assembly, device, or method that prevents the backflow of water in water systems. The backflow assembly or device may be installed at the water connection between the city main and a building, or it may be installed at the source of possible contamination or pollution.

A backflow prevention assembly is a device which uses spring loaded check valves to prevent polluted or contaminated water from flowing backwards. Some assemblies eliminate backflow by discharging used water to the ground. 

Without backflow prevention devices and assemblies, the potable water supply can become contaminated by any customer in the system. At the 1933 Chicago World’s Fair, 98 people died from Dysentery due to sewage from the toilets that backed up into the water system. More recently, the neighbors to a food processing company discovered that their water was tainted with apple juice; not a health hazard to most but the coffee probably tasted funny. These events and many others like them are the result of cross connections.  Examples of potential cross connections include automatic lawn sprinkler systems, fire sprinkler systems, carbonated beverage machines, carwashes, and dry cleaners. Even in your own home, you can unwittingly create a cross connection by putting the garden hose in a swimming pool, pet’s water bucket or fish tank to fill it or putting it down the drain to flush out debris when it’s backed up or connecting your garden hose to a plant fertilizer or bug spray unit.

Backflow prevention assemblies have internal seals, springs and moving parts that are subject to wear, fatigue and fouling. Routine testing helps ensure that the mechanical device is in proper working order.

Yes, standard testing procedures require that the water service be turned off for testing. Depending on the type of assembly, the time needed is from 10 to 30 minutes. Additional time may be needed if repairs are required.

No.  Only testers who have passed a written and practical examination and hold a valid State of Washington Department of Health issued backflow assembly tester (BAT) card can test backflow assemblies.      

Permits are easily obtained online at www.mybuildingpermit.com and can be issued at the time of application.  

It is your responsibility to have the assembly tested when it is installed and annually thereafter.  A copy of the test report showing that the assembly passed will need to be forwarded to the Cross-Connection Control Program Office at cccprogram@kirklandwa.gov . The state requires that water purveyors, testers and customers test records be kept for five years.

It is a special report form approved by the State of Washington and the City used by certified backflow assembly testers to log test results.  The tester you hire will supply the report form.