Using Vacuum Breakers to Prevent Backflow with Garden Hoses

Richard L. Parish, PhD, PE

You probably use a garden hose connected to your home water supply for irrigation of your lawn and garden, washing your car, bathing your pet, and perhaps applying pesticides. In all of these cases, the potential exists for backflow of contaminated water into your home and from there, into the municipal water supply or your well. Using a simple, inexpensive vacuum breaker on your hose bibbs can help prevent this hazard.

What is Backflow? Backflow is backward movement of water from your garden hose back into the water supply. Backflow can occur if the pressure in the home (or municipal) water system suddenly drops. This can occur if there is a sudden demand on water in the system due to a leak, fire trucks pumping from hydrants, or a system pump failure. Backflow can also occur if you leave a hose connected to a hose bibb and the hose bibb turned on while a valve at the end of the hose is closed. In this case, the hose will be fully pressurized. Even a small drop in system pressure will then cause water to backflow. Even if system pressure does not drop, a hose lying in the sun will heat up and can cause the pressure in the hose to increase to a level greater than system pressure and thus cause backflow.

Backflow Prevention with a Vacuum Breaker: A hose vacuum breaker (HVB) is a simple device that screws onto the hose threads on your hose bibb. It, in turn, has male hose threads onto which you can attach your garden hose. Use of your garden hose with an HVB is no different than without one. The HVB allows water to flow out normally, but opens and vents to the atmosphere if a pressure reversal occurs. The cost is typically only $5-10. HVBs are required by many plumbing codes.

Installation: Installation consists of simply screwing the HVB onto the hose bibb. The HVB should be at least 6 inches above the ground so that there is no risk of it being in a puddle of water. Note that most HVB’s are designed to be easy to install, but difficult to remove!

Maintenance: Very little maintenance is needed. Your HVB(s) should be inspected occasionally to be sure they are working and not stuck. To check the operation of an HVB, hook a hose to the HVB and install a valve or nozzle that can be closed on the end of the hose. Close the valve on the end of the hose and open the hose bibb. Then, close the hose bibb while the hose is pressurized. In a few seconds, you should see a small spray of water from the HVB as the hose pressure is released. If the HVB fails this test or if it leaks in normal operation, it may need to cleaned or replaced. Hard water or contaminants in the water can cause the mechanism to stick or bind. It may be possible to manually move the components enough to free them up; if not, the HVB will have to be replaced. Because they are difficult to remove, this may entail replacing the hose bibb also.

There are many ways that water in a garden hose can be drawn back into your water supply. Hose vacuum breakers are a simple and inexpensive way to reduce the risk of contaminating your home water supply (or the municipal water supply). They are an important step in protecting your family’s water.