Why the village sent you that letter, what the test involves, and what happens if the device fails
A backflow preventer is a valve on your water line that only lets water flow one direction: from the street into your property. Its job is to make sure water that’s been in your lawn sprinklers, your pool, or a piece of commercial equipment can never get pulled back into the drinking water supply. If you have one, Illinois requires it to be tested every year by a certified inspector, and your village requires proof.
If you got a letter from the village about backflow testing, that’s what it’s about. Here’s what you need to know.
What is a backflow preventer and why do you need one?
Normally water pressure in the street pushes water into your house and it never comes back. But pressure in the main can drop suddenly: a water main breaks, a hydrant gets opened, a fire truck hooks up down the block. When that happens, water can get siphoned backward out of your pipes and into the public supply. If your pipes are connected to anything besides clean water, like an irrigation system that’s been sitting in fertilized soil, a pool with chemicals in it, or a fire sprinkler system full of stagnant water, that’s what goes back into the main. Then it comes out of your neighbor’s faucet.
Any point where drinking water piping connects to something that isn’t drinking water is called a cross-connection. A backflow preventer sits at that connection and blocks the reverse flow. The most common one on the North Shore by far is the RPZ valve on a residential lawn sprinkler system.
This isn’t theoretical. In 1933, during the World’s Fair in Chicago, a cross-connection at a downtown hotel let sewage into the drinking water and caused an outbreak of amoebic dysentery that sickened more than a thousand people and killed nearly a hundred. Modern cross-connection rules came out of that.
RPZ valve vs. double check valve
There are two common types of backflow assembly, and the hazard decides which one you need.
A double check valve assembly has two spring-loaded check valves in a row. If one fails, the other holds. It’s used for low-hazard connections where the worst case is a nuisance, not a health risk.
A reduced pressure zone (RPZ) assembly has the same two check valves plus a relief valve between them. If either check leaks, or pressure in the main drops below pressure in your pipes, the relief valve opens and dumps the water out onto the floor or into a drain instead of letting it go backward. It’s the required device for high-hazard connections: irrigation systems, pools, fire sprinklers, and most commercial equipment. That’s why an RPZ has to be installed somewhere it can drain, with clearance around it and, indoors, a floor drain that can handle the discharge.
If your RPZ occasionally spits water out of the bottom, that’s the relief valve doing its job during a pressure change. If it drips constantly, a check valve is fouled or worn and it needs service.
When does a backflow preventer have to be tested?
- When it’s first installed.
- After any repair or rebuild.
- At least once a year after that, every year.
That’s the Illinois standard, and every North Shore village enforces it. Most villages send annual notices with a deadline. Miss it and you’re looking at fines, and eventually a shutoff notice, because an untested device is treated as an unprotected cross-connection.
For irrigation systems, the practical time to test is in the spring when the system is turned on for the season. The RPZ has to be winterized in the fall with the rest of the sprinkler system, so a spring test confirms it survived the winter and is working before it runs all summer.
What happens during a backflow test?
The test takes about 30 to 45 minutes if the device is accessible and working.
- The tester connects a calibrated differential pressure gauge to the small test cocks on the assembly.
- The shutoff valves on either side are closed to isolate the device.
- Each check valve is tested to confirm it holds pressure in the right direction, and on an RPZ the relief valve is tested to confirm it opens at the right pressure differential.
- Readings are recorded on the official test form.
A device fails when a spring has weakened, a rubber disc has worn or scaled up (common with our water), or debris has kept a check from seating. Most failures are fixed by rebuilding the assembly with a kit: new checks, seals, and springs. That’s usually done on the same visit, then the device is re-tested. A device that’s cracked from freezing or too corroded to rebuild gets replaced.
After a passing test, the tester signs the report and it goes to the village. Some villages want it mailed or emailed to the water department; several North Shore villages use a third-party tracking service and the report gets filed there. Either way, the test isn’t done until the village has the form.
Who can perform a backflow test in Illinois?
Not just any plumber. Illinois requires the tester to be a licensed plumber who also holds a Cross Connection Control Device Inspector (CCCDI) certification from the Illinois EPA. The certification number goes on the test report, and the village checks it. Ask whoever you hire for their CCCDI number before they show up.
Installing a new backflow preventer
You’ll need one installed if you’re putting in a lawn sprinkler system, an auto-fill pool, a fire sprinkler system, or commercial equipment with a water connection. The village plumbing permit will require it, and the inspector will check that it’s the right type for the hazard, the right size for the line, installed at the right height with clearance for testing, and able to drain if it’s an RPZ.
The two mistakes we see most on installations done wrong: an RPZ mounted where it can’t drain, so when the relief valve opens it floods a basement, and an outdoor RPZ left in place over winter with water in it, which cracks the body. Both are avoidable.
Frequently asked questions
Why did I get a backflow testing notice from my village?
Because the village has your property on record as having a backflow device, usually because of a sprinkler system, and Illinois requires an annual test. The notice has a deadline. Schedule the test, and make sure the report gets filed.
What’s the difference between a double check valve and an RPZ?
A double check has two check valves and is for low-hazard connections. An RPZ adds a relief valve that dumps water if a check fails or pressure reverses, and it’s required for high-hazard connections like irrigation, pools, and fire sprinklers.
Can any licensed plumber test my backflow preventer?
No. In Illinois the tester has to be a licensed plumber with a CCCDI certification from the Illinois EPA. The certification number goes on the report.
How long does a backflow test take?
About 30 to 45 minutes for a working device. Longer if it needs a rebuild, which is usually done on the same visit.
What happens if my backflow preventer fails the test?
It gets rebuilt with new internal parts and re-tested, usually the same day. If it’s cracked or too corroded to rebuild, it’s replaced. Either way, the village gets a passing report when it’s done.
Does my RPZ need to be winterized?
Yes, if it’s outdoors or in an unheated space. It’s drained and blown out with the rest of the irrigation system in the fall. An RPZ that freezes with water in it cracks, and that’s a replacement.
Backflow testing and installation on the North Shore
Biagi Plumbing has been installing, testing, and repairing backflow preventers for homes and businesses on the North Shore since 1989, in Highland Park, Evanston, Glenview, Wilmette, Winnetka, Glencoe, Lake Forest, Lake Bluff, Deerfield, Northbrook, Buffalo Grove, Libertyville, and the surrounding communities.
If you’ve got a testing notice from the village or you’re adding a sprinkler system or pool, call Biagi Plumbing at (847) 512-8921. Our testers are Illinois EPA-certified, we carry rebuild kits on the truck, and we make sure the report gets to the village so you’re done when we leave.