Understanding Backflow


Can water flow backwards?

Yes.  Water, like electricity, takes the path of least resistance from a higher pressure to a lower pressure.  Normally, water flows directly from our mains to your property, but in certain situations, such as a main break, water can flow back into the distribution system.

What harm could that cause?

Plenty.  When water is delivered to your property it is exposed to many different types of fixtures, including sprinklers, washing machines, hose-bibs, kitchen faucets, tubs, showers, and toilets.  For industrial users, the system may be attached to boilers, photo processing equipment, chemical mixing tanks, chillers, water towers, pressure pumps, healthcare and laboratory equipment, etc.  Connections between the potable water system and potential sources of pollution, or contamination, are called "cross connections."  When backflow occurs through a cross connection, there is a chance that contaminants can be drawn into the public water system.

Do these backflows really occur?

Yes.  Around the country, cross connections and backflow are responsible for many cases of illness, injury, and even deaths every year.  Recognizing this hazard, the Washington State Legislature instituted WAC 246-290-490 to require water purveyors such as NPW to protect the public water system against cross connections and backflow.

NPWD's Cross Connection Control Program

We at North Perry Avenue Water District work very hard to provide you with quality drinking water. One of the ways we do that is through our cross connection control program. Fortunately, there have not been any documented backflow incidents impacting our local water system, and we are taking steps to keep it that way.  NPWD's Cross Connection Control Program, which fully satisfies the requirements of Washington Administrative Code 246-290-490 and NPWD's resolution 590, 644, and 650, begins with the identification of businesses, industries, and residential areas that are likely to contain cross connections.  As mandated by the state, an onsite survey of the property is conducted by one of our certified Cross Connection Specialists.  They often suggest ways to protect the internal water system against backflow and, if necessary, ask the consumer to install a backflow prevention device at the meter that will protect the public water supply. After the device is installed, the law requires that it be tested by a certified tester at least once a year. If you feel you have a possible cross connection occuring, please feel free to give us a call.

Backflow Hazards at Home

How many times have you put a garden hose in a bucket of soapy water to wash the car?  Or sprayed insecticide with a garden hose sprayer?  Or attached a hand spray attachment to the kitchen faucet to wash your hair or the dog?  Or have an irrigation system installed? These seemingly harmless actions create cross connections that could endanger the health and safety of you, your family, and your neighbors.

The danger comes when the hose comes in contact with a harmful substance. If the pressure in the water main drops while the hose is submerged in contaminated water, then the water (and whatever is in it) could be sucked back into your pipes and the drinking water supply.  Another example involves irrigation systems. Fertilizer, animal waste or other hazardous chemicals can be sucked in through the sprinkler heads if the water pressure drops. Water pressure drops are not uncommon.  They can occur when hydrants are opened to fight fires or during repairs to a broken water main.

Fortunately, keeping your water safe from these contaminants is easy, as illustrated here:

backflow diagram


Private Wells

Backflow can also occur in the absence of a water main pressure drop. For example, some homes have backup water systems supplied by private wells or springs. If these systems are connected and overcome the pressure in the public water supply, backflow will occur. They pose a hazard to the potable water system and must be equipped with proper backflow prevention devices.

Commercial-Industrial Requirements

In commercial or industrial situations, water often comes in contact with different types of hazardous substances, whether it be for mixing, diluting, flushing, or cleaning. North Perry Avenue Water District requires all commercial services to install either an Air Gap, Reduced Pressure Backflow Assembly or both.

We realize that there is some inconvenience and often some expense in complying with these requirements. Our Cross Connection Specialists will make every effort to work with you to facilitate the installation and testing of the appropriate device if needed.


Please contact Courtney Little, Cross Connection Control Specialist at our office with any questions and prior to any installation.