Backflow Preventers and Annual Testing in Montana

What does a backflow preventer do?

It stops water from flowing backwards out of your irrigation system into the drinking water supply. Missoula Water's Cross-Connection/Backflow Protection Program explains that backflow happens when pressure in the distribution system drops, siphoning water from a customer's system back into the main, or when a customer's system is pressurized enough to overcome the main's pressure. Either way, anything in contact with the water through a cross-connection can be drawn in. The program defines water in an irrigation system as non-potable.

An irrigation system is an obvious risk: its heads sit in soil that may hold fertilizer, herbicide, pet waste and standing water. The Montana Department of Environmental Quality's drinking water rules page puts it plainly: backflow into a public water system can pollute or contaminate the water in that system.

What types of backflow preventers are used on irrigation?

Missoula Water's program defines several. A reduced pressure zone assembly (RP) has two independently operating check valves with a relief valve between them and protects against all levels of hazard under both backpressure and backsiphonage. A double check valve assembly (DCA) has two check valves and is limited to non-health hazards. A pressure vacuum breaker (PVB) has a loaded check valve and an air inlet valve, and protects only against backsiphonage, not backpressure. An atmospheric vacuum breaker (AVB) is the simplest and also protects against backsiphonage only, with no valves allowed downstream of it.

DEQ draws a further line between an assembly and a device. An assembly can be tested and repaired in line and has isolation valves and test ports; a device cannot be tested in line, has limitations and may not be approved by the department. The air gap, a physical separation, is what DEQ calls the ultimate backflow protection.

What does Missoula require for lawn sprinkler systems?

Missoula Water's program summary says approved backflow preventers are required to be installed, maintained and tested annually on all underground irrigation systems. Its table of required protection lists premises, including single-family residences, with underground irrigation systems as needing an RP, and says a properly installed AVB or PVB may be provided instead with written approval from Missoula Water. Premises with irrigation systems into which fertilizers, herbicides or pesticides are or can be introduced are listed as needing an RP. The program also requires backflow protection for all commercial projects, multifamily developments of four units or larger, and all properties where auxiliary water supplies exist.

The program was adopted by the Missoula City Council on June 11, 2018, is approved by DEQ, and the version we read was revised February 16, 2022. If you are outside Missoula Water's service area, in Lolo, Florence, Stevensville, Hamilton or elsewhere in the Bitterroot, ask your own water provider what it requires; we have not found a single valley-wide rule.

How often does a backflow assembly need testing?

At least once a year in Missoula, plus extra tests at specific times. The program says assemblies must be tested at least annually and immediately after installation, relocation or repair, by a person holding a current certificate from a state certification program or the American Society of Sanitary Engineers, and that Missoula Water may require more frequent testing. A field test report must be submitted to Missoula Water each time an assembly is tested, relocated or repaired, and the costs of testing, repair and maintenance are borne by the water user.

DEQ describes the same schedule as industry practice statewide: every assembly tested by a certified tester after initial installation, after repairs of any kind, and at least once annually. DEQ accepts testers certified through a state program, the American Society of Sanitary Engineers or the American Backflow Prevention Association.

What happens if the test is not done?

Missoula's program spells out the sequence. Missoula Water sends a written notice when a test is due, giving 30 days. If the test is not done, a second notice gives 2 weeks. If there is still no action, the utility hand-delivers a 24-hour notice of discontinuing service and may terminate water service until the assembly is tested or repaired and the forms are submitted. That is service to the property, not just the sprinklers, so the notice is worth acting on.

Who can test a backflow preventer in Missoula?

A certified backflow assembly tester. Missoula Water publishes a list of certified testers on its Backflow page, with phone numbers, and the program says the utility will provide the list on request. HJ Property Care is not a certified backflow tester and is not on that list. We install, repair, winterize and start up irrigation systems around the backflow assembly, and we coordinate with your tester so the annual test happens with the system charged and running. If an assembly fails its test, the program requires it to be serviced, overhauled or replaced, and repairs must be done by someone meeting state and local requirements; it must then be retested.

Where should the assembly be installed?

Missoula's program is specific. A PVB must be installed at least 12 inches above all downstream piping and the highest outlet, vertically, where water spilling from its air inlet is not a problem, and protected from freezing. An RP must be installed horizontally, from 12 to 30 inches above grade measured from the bottom of the assembly, with at least 12 inches of side clearance, adequate drainage in case it discharges, and protection from freezing. A DCA below grade must sit in a vault with set clearances. Everything has to be accessible for testing. On a sloped lot, the PVB height rule matters: the PVB has to sit above the highest head it serves.

The program also requires that valves and fittings in contact with potable water meet the federal lead-free standard of a weighted average lead content below 0.25 percent.

Why is a vacuum breaker not allowed everywhere?

Because it only protects against one of the two ways backflow happens. Missoula's program says a PVB protects against backsiphonage only and that in no case should a PVB be used if backpressure could develop in the downstream piping; it sets the same limit for an AVB, and adds that an AVB must not have any valves downstream and must not be under continuous pressure for more than 12 consecutive hours. Backpressure can come from a booster pump, from a second water source tied into the system, or from piping that runs uphill of the device. That is why Missoula lists the RP as the default for underground irrigation and allows a PVB or AVB only with the utility's written approval, and why it requires an RP where chemicals can be injected into the irrigation water. If a fertilizer injector or a well tie-in is part of your plans, settle the assembly type with your water provider before it is installed.

How does winter damage a backflow preventer?

Freezing water. Our irrigation systems page notes that the backflow preventer is usually the most expensive single component on a residential system because it is brass and exposed, and that it almost always fails from water left inside over winter. Colorado State University Extension's winterization guide adds two cautions: PVB and RP devices must never be blown out with compressed air, because their internal rubber seals can melt, and after the zones are blown out the PVB's ball valves and test cocks should be exercised and left half-open for winter, with an RP's isolation valves left at about 45 degrees. Our sprinkler blowout service follows that sequence, and the companion winter guide on frozen backflow and irrigation damage covers what to do when one cracks.

What should you do in spring?

Close the test cocks and ball valves before pressurizing, then open the ball valves slowly, as CSU advises, to avoid water hammer. If Missoula Water has notified you that a test is due, schedule it once the system is charged. Our spring startup guide walks through the full sequence.

Can HJ replace or relocate a backflow assembly?

We handle backflow preventer repair and replacement as part of our sprinkler repair work, built to the provider's installation rules, and Missoula's program then requires a test by a certified tester before and after the assembly goes into service. If you are not sure what assembly you have or whether it was ever approved, start with your water provider. This guide is part of our Montana Landscaping, Lawn & Irrigation Guide. Call HJ Property Care & Tree Service at (406) 215-7319 or request a free estimate. We work across Missoula and Ravalli counties, from Missoula and Lolo to Florence, Stevensville, Corvallis, Victor, Hamilton and Darby.

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