A notice arrives telling you your backflow assembly is due for its annual test. Most people have never looked at the thing. It is the brass device standing above ground near where your irrigation system leaves the house, and it is the only part of your sprinkler system that protects your drinking water.
This page covers what the city requires, why irrigation systems in particular get this treatment, what the test actually measures, how these assemblies fail here, and what happens when one does not pass.
What St. George requires
The city's backflow page lists four things asked of homeowners. Install approved backflow assemblies on all outside watering systems. Protect the assemblies from freezing. Have it tested annually. And maintain hose bib vacuum breakers on exterior garden hose connections.
The ordinance behind it is St. George City Code Title 8, Chapter 2, Backflow and Cross Connections. Section 8-2-4 covers when a device or assembly is required, section 8-2-5 covers testing and inspection, and section 8-2-16 is the penalty section.
Section 8-2-4(A) puts the duty on the property owner in plain words. The owner must "purchase, install, test, inspect and maintain backflow prevention devices or assemblies wherever it will be possible for used, unclean, polluted or contaminated water ... to enter any portion of his potable water system." That is the whole legal structure in one sentence. The device is yours, the maintenance is yours, and the test is yours to have done.
Water Services is at 620 East Waterworks Drive, 435-627-4802. They are the right call for how the city wants the test result handled for your address, and for anything on the street side of your meter.
Why irrigation systems specifically
An irrigation system is a permanent, pressurized connection between your drinking water and an environment that is contaminated by definition. Emitters and spray heads sit in soil that holds fertilizer, herbicide, pesticide and animal waste, and after a cycle they often sit in standing water.
Normally pressure pushes outward, from the main to the house to the sprinkler head, and nothing travels backward. Then something drops the pressure in the street: a hydrant flush, a water main break, a fire flow, a pump station event. The gradient reverses, and the plumbing does the obvious thing. It draws water backward, out of the soil, through the heads, into your house and into the street main.
That is the part worth sitting with. Backsiphonage does not require anything to go wrong at your house. It only requires something to go wrong at the street. The city frames it the same way: backflow occurs when water pressure drops, potentially allowing contaminated water from irrigation systems to flow back into the municipal supply, and the program exists to prevent contamination of the culinary water system.
The assemblies, and where each one belongs
Not every device on this list is testable, and not every device is acceptable for every hazard. The type you have should match the hazard your system presents.
| Device | Protects against | Testable | Typical use |
|---|---|---|---|
| Hose bib vacuum breaker | Backsiphonage at a hose connection | No | Required by St. George on exterior garden hose connections |
| Atmospheric vacuum breaker (AVB) | Backsiphonage only | No | Must sit at least 6 inches above the flood level rim of the fixture or device it serves, measured to the device's critical level, with no valve downstream, and never under continuous pressure for more than 12 consecutive hours |
| Pressure vacuum breaker (PVB) | Backsiphonage only, not backpressure | Yes | The standard residential irrigation assembly in Utah. Must sit at least 12 inches above all downstream piping and the highest point of use, installed vertically, never below grade or in a pit. Above grade, so freeze vulnerable |
| Spill resistant vacuum breaker (SVB) | Same as a PVB, without spilling on test | Yes | Indoor locations where a PVB's spill would cause damage |
| Double check valve assembly (DCVA) | Backsiphonage and backpressure, non health hazard only | Yes | Fire sprinkler systems without chemical additives, some commercial premise isolation |
| Reduced pressure principle assembly (RPZ) | Backsiphonage and backpressure, including health hazards | Yes | Irrigation with fertilizer or chemical injection, boilers with treatment chemicals, commercial process water |
| Air gap | Everything. The only non mechanical protection | Not applicable | Two pipe diameters, minimum 1 inch. St. George requires a permanently affixed air gap on every chemical vehicle that takes water from the city supply |
The fertigation trap
Here is the change that catches homeowners, and it is worth knowing before you buy anything at a garden center.
An irrigation system on its own is generally treated as a pollutant hazard, not a health hazard, and a pressure vacuum breaker is adequate protection for it. Add a fertilizer or chemical injector to that system and it becomes a contaminant hazard under backpressure. The required protection goes up with it, from a PVB to a reduced pressure principle assembly.
People install fertigation kits on a Saturday without any idea they have changed what the code requires at their meter. If you have one, or you are thinking about one, that is the conversation to have first.
One siting rule that goes with an RPZ: it discharges out of a relief port when it does its job, so it has to be above grade with an air gapped relief drain. An RPZ in a pit that can flood is worse than no assembly at all, because a discharging relief valve sitting under water creates exactly the cross connection the assembly was installed to prevent.
What happens during the test
The tester closes the isolation valves, attaches a differential pressure gauge to the test cocks on the assembly, and measures whether each check valve holds the required pressure difference in the correct direction. On an RPZ the relief valve is also checked, to confirm it opens and closes at the right differential. Your irrigation is shut down for the few minutes this takes.
The whole test is a measurement of numbers a device either makes or does not make. There is no judgment call in it, which is why it is worth two questions before anyone touches yours. Ask what backflow certification the tester holds. Ask when the gauge was last calibrated. A test report is only as good as the gauge that produced it, and a gauge that has drifted will pass an assembly that should fail and fail one that should pass.
Call Water Services at 435-627-4802 to confirm how the city wants your result submitted, and keep a copy. It is a one page document and it is the only proof you have that the device on the side of your house works.
Freezing, which is how most of these die here
A PVB or an RPZ holds standing water in its body, its bonnet, and its check chambers, above ground, out in the open. Water expands about 9 percent when it freezes. With nowhere to go, it splits the brass body, cracks the bonnet, or ruptures the check assembly. A cracked body is not repairable.
The local pattern is distinctive, and it is worth understanding rather than just being told to winterize. St. George averages a January low of 28.4°F, sees roughly 60 mornings a year at or below freezing, has a historical freeze window running November 12 to March 14, and holds a record low of minus 11°F. Most of those freezes are short overnight dips right at 32°F, not sustained hard freezes.
That means the assembly that cracks here is usually not one that was left running all winter. It is one that was nominally winterized but had water trapped inside it: blown out but never drained, drained but with the test cocks left closed, or ball valves left fully open or fully closed so a slug of water sat inside the ball.
The order that avoids that: shut the isolation valve upstream, open both test cocks and any bleed, then set both ball valves to roughly 45 degrees so nothing is trapped inside the ball body. Blow out the irrigation zones with compressed air at 50 psi or less, never at high pressure through the assembly's internals. Then insulate or cover it, secured well enough to survive the wind.
The 45 degree step is the one that gets skipped, and it is the most common cause of a cracked valve.
What a failed test means
A failure means the assembly did not hold the required differential pressure. A check valve leaked backward, or on an RPZ the relief valve did not open or close at the correct differential. It is a specific mechanical finding, not an opinion.
The usual causes are ordinary. Debris on a check seat, which is sand, scale flakes or pipe chips. A worn poppet or disc rubber. A weak or broken spring. A fouled relief valve. A leaking isolation valve that looks like a check failure until someone rules it out. Or a freeze cracked body, which is the one cause with no repair.
Most failures are rebuilt with the manufacturer's kit of springs, discs, seats and O rings, and rebuilding is normally the right answer. Replacement is correct in three cases: the body is cracked, the assembly is obsolete and parts are no longer available, or the assembly is the wrong type for the hazard. That last one is the fertigation case, and a failed test is the right moment to correct it rather than rebuild the wrong device.
After any repair or relocation, the assembly is tested again. A rebuild that has not been retested is a rebuild nobody has verified.
What we’d do at your house
We test with a gauge, we show you the numbers it produced, and you get the report.
If it fails, we tell you whether it is a rebuild or a replacement and why, before we quote either one.
If you have added a fertilizer injector, we will tell you the assembly type has to change, even though that is the more expensive answer.
We winterize with the ball valves set part open, because that is the step that keeps the body from cracking in February.
We look at your hose bib vacuum breakers while we are there, since the city asks for those too and they cost almost nothing.
We are not going to sell you an RPZ for a system that only needs a pressure vacuum breaker.
Sources
What this page says comes from the documents below, read in full. It describes them. It is not legal advice. Confirm with your association, your city, or an attorney before you act.
- City of St. George backflow information page (approved assemblies on all outside watering systems, protect from freezing, annual test, hose bib vacuum breakers; the city's own description of backflow; Water Services, 620 East Waterworks Drive, 435-627-4802) 01-plumbing-corpus.md §7.1, §7.2, §7.3
- St. George City Code Title 8, Chapter 2, Backflow and Cross Connections, including section 8-2-4 (when required), 8-2-5 (testing and inspection), 8-2-16 (penalty), and the quoted text of 8-2-4(A) 01-plumbing-corpus.md §7.3
- St. George City Code 8-2-4(B)(3), air gap requirement on chemical vehicles 01-plumbing-corpus.md §7.1
- Assembly types, hazard levels, installation heights, and the pollutant to contaminant escalation when chemical injection is added 01-plumbing-corpus.md §7.1, §7.2
- Freeze failure mechanism, the local shallow freeze pattern, and the winterization sequence 01-plumbing-corpus.md §7.4, §8.3
- St. George climate data (January average low 28.4°F, roughly 60 freezing mornings a year, freeze window November 12 to March 14, record low minus 11°F) 01-plumbing-corpus.md §7.4, §8.3; 05-environment-water-geology-corpus.md §3.3
- Failed test causes, rebuild versus replace, and retest after repair or relocation 01-plumbing-corpus.md §7.5