Backflow testing is the annual check that proves the device protecting the public water supply at your property still works. Every irrigation system, fire line and commercial connection in San Antonio has an assembly on it whose only job is to stop water flowing the wrong way, and because that device is mechanical it is required to be tested by a licensed tester at intervals your water provider sets. Silverback Plumbing and Drain tests, repairs and replaces backflow assemblies, and files the paperwork so you are not chasing it.
A backflow preventer is the only thing standing between the fertiliser in your irrigation line and the drinking water in the street. It is mechanical, it wears, and testing is how anyone knows it still closes.
What backflow actually is
Water in a supply main is supposed to travel one way. Backflow is what happens when it does not, and there are exactly two mechanisms behind it.
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Back-siphonage
Pressure in the main drops — a burst somewhere, a hydrant opened for a fire — and the resulting suction pulls water back out of a property into the street.
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Back-pressure
Pressure on the property side rises above the main, from a pump or a boiler, and pushes water back the other way.
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Why irrigation is the classic case
Sprinkler heads sit in soil that may carry fertiliser, herbicide and animal waste. Siphon that back into the main and it reaches the neighbours.
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Why a pool or a boiler counts
Chemical treatment and closed heating loops are both cross-connections. Each needs the right assembly and each is subject to backflow testing.
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Why it is not optional
Texas requires assemblies protecting a health hazard to be tested by a licensed tester, and water providers hold the records.
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Why it fails quietly
A backflow preventer that has stopped sealing looks exactly like one that works. Only a gauge test tells you which you have.
Who needs backflow testing, and how often
Requirements are set by the Texas Commission on Environmental Quality and administered locally by your water provider, so the interval and the paperwork depend on who supplies you. The pattern below covers most San Antonio properties.
| Property | Typical requirement |
|---|---|
| Home with an irrigation system | Assembly tested at installation and then on the interval your provider sets, commonly annually |
| Home with a pool, well or boiler | Assembly required on the cross-connection, with backflow testing on the same cycle |
| Commercial premises | Annual testing, records held by the provider, and testing again after any repair |
| Fire sprinkler line | Annual, and coordinated so the system is not left unprotected |
| Any assembly just repaired or moved | Tested again immediately. A repair without a retest is not a completed job |
If you are unsure whether your property is on a testing programme at all, the fastest answer is usually a line on your water bill or a notice from the provider. We can also check the assembly on site and tell you what it is and what it is subject to.
The four assemblies you will meet
Which device is on your property decides how the backflow testing is carried out and what a failure means.
| Assembly | Where it is used | Notes |
|---|---|---|
| Atmospheric vacuum breaker | Individual hose bibs and simple outlets | Not a testable assembly. Protects against siphonage only, and must sit above the outlet |
| Pressure vacuum breaker | The common residential irrigation device | Testable, above ground, and the one that splits in a hard freeze |
| Double check valve | Lower-hazard commercial and fire lines | Testable, can be installed below grade in a vault |
| Reduced pressure zone | High-hazard connections — chemicals, boilers, reclaimed water | Highest protection, must be above ground, discharges to atmosphere when it fails |
The one people trip over is the reduced pressure zone assembly. It is designed to dump water on the ground when an internal check fails, which is a feature rather than a fault — it is telling you loudly that protection has been lost. A puddle under an RPZ is a call, not a mystery.
What the annual backflow testing involves
Backflow testing takes fifteen or twenty minutes on a typical residential assembly. Here is what happens in that time.
- We identify the assembly — make, model, size and serial number — because the report has to name it and the provider matches it against their records.
- Water downstream is shut off. On an irrigation system that is a brief interruption; on a commercial or fire connection it is coordinated in advance so nothing is left unprotected.
- A calibrated differential gauge is connected to the backflow testing cocks on the assembly.
- Each check valve and, on an RPZ, the relief valve is tested in turn against the pass criteria for that device type. The readings are recorded as they are taken.
- The assembly is returned to service and normal operation is confirmed before we leave.
- The report is completed, signed under the tester licence, and submitted to your water provider. You get a copy for your own records.
Our gauges are calibrated annually and the certificate is available on request, which matters because a provider can reject a backflow testing report submitted on an uncalibrated gauge.
Reading your backflow testing report
The certificate you get back is a one-page document and it is worth knowing how to read it, because it is the thing a provider, a buyer or an inspector will ask for.
The top half identifies the assembly: make, model, size, serial number and its location on the property. Those five fields are how your water provider matches the backflow testing report to the device on their register, and a mismatch is the most common reason a report gets bounced back.
The middle records the readings — the pressure differential across each check valve, and on a reduced pressure zone assembly the point at which the relief valve opened — against the pass criteria for that device. Numbers rather than a tick, so anyone can see the margin rather than just the verdict.
The bottom carries the date, the tester licence number, the gauge serial and its calibration date. A backflow testing report missing any of those is not a valid certificate, whoever issued it, and that is worth checking on any report you inherit with a property.
It failed. What now?
A failed test is common and it is rarely terminal. These assemblies are mechanical and the parts that wear are replaceable.
Most failures are a check valve that no longer seats, usually because grit or scale has lodged on the sealing surface, or a rubber component that has hardened with age and heat. A repair kit for the specific make and model replaces the springs, discs and seals, and the assembly goes back to as-new performance.
Replacement becomes the answer when the body itself is damaged — a freeze split is the usual cause here — or when the assembly is obsolete and parts are no longer made. On an older device it is worth asking the question early, because a rebuild on something unobtainable is money spent twice.
Either way, the work is followed immediately by another test. Backflow testing after a repair is not optional and it is not an upsell: an assembly that has been opened is not certified until it has been retested and the new report filed.
What we look at beyond the gauge readings
A pass on the gauge is not the whole of a competent backflow testing visit. An assembly can test perfectly and still be installed in a way that will not protect anything.
Height and orientation come first. A pressure vacuum breaker has to sit at least twelve inches above the highest downstream outlet, and a surprising number in this city are mounted too low — usually because a sprinkler head was added uphill years after the assembly went in. The device passes, and it cannot do its job. That gets flagged in writing.
Then the practical things around it. Are the shutoffs on either side actually operable, or seized? Is a below-grade assembly sitting in a vault full of water, which is a contamination path in itself? Is there a cover on it before winter? Has anything been added downstream since the last backflow testing that changes the hazard rating and therefore the type of assembly required?
None of that appears on a test report, and all of it decides whether the protection is real. We put it in the notes that come back to you with the certificate.
The week after a freeze is our busiest week
A pressure vacuum breaker sits above ground, outdoors, usually against a wall with no insulation on it. San Antonio gets a hard freeze rarely enough that nobody prepares for it and often enough to split a great many of them at once.
The damage is predictable: water trapped in the bonnet expands and cracks the body or blows the poppet apart. It shows as a fountain the moment the system is next pressurised, which for most households is the following spring rather than the day it happened.
Two things prevent nearly all of it. Shut the irrigation supply and drain the assembly before the first hard freeze of the season, and fit an insulated cover on anything that stays charged. Neither is expensive and both are quicker than the replacement they avoid.
If yours has already split, replacement plus backflow testing is a single visit. We keep the common residential sizes on the van through the winter for exactly this reason.
What sets the price
Routine backflow testing is one of the more predictable jobs we do. These are the things that change it.
| Factor | Why it matters |
|---|---|
| Number of assemblies | Testing several on one site at one visit is far cheaper per device than separate call-outs |
| Assembly type and size | A residential pressure vacuum breaker and a large commercial RPZ are different jobs with different time on site |
| Access | A device in a below-grade vault needs the vault opened, pumped out if flooded, and made safe |
| Repair after a failure | Rebuild kits are priced by make and model, and the retest is included rather than billed again |
| Scheduling constraints | Fire lines and commercial sites often need testing outside business hours to avoid interrupting operations |
Commercial sites, property managers and new installations
For anyone holding several addresses, backflow testing is an annual compliance chore with a deadline attached, and the cost of getting it wrong is a notice from the provider rather than a plumbing failure.
We hold the assembly details for every device on your sites — location, make, model, serial and last test date — and come back on the cycle rather than waiting for you to remember. Reports go to the provider and to whoever you nominate, and failures come with a repair quote attached rather than a second appointment to find out.
On new installations the sequence is fixed: the assembly is fitted at the correct height and orientation for its type, and it is tested and reported before it goes into service. An assembly installed and left untested is not compliant no matter how new it is, and it is one of the more common things we find when we take over a site.
Backflow testing across San Antonio and the surrounding towns
We test across San Antonio, Helotes, Boerne, Bulverde, Schertz, Converse, Stone Oak, Alamo Ranch and Somerset. Residential irrigation assemblies are the bulk of it, with commercial and fire line work alongside.
If the assembly failed because it froze, or because grit got into it, the wider water question is worth a look too — whole-house filtration deals with the sediment that shortens the life of every valve in the house.
Records, renewals and not being chased
The administrative half of backflow testing is where most of the friction actually sits, and it is the part we take off you.
Every test we carry out is logged against the assembly — make, model, serial number, location, date and result — so the record follows the device rather than the invoice. When the next cycle comes round we contact you rather than waiting for a notice from your water provider to do it.
Reports are filed with the provider on your behalf and a copy goes to you the same day. If you manage property, copies go to whoever you nominate as well, in whatever form your compliance file needs.
The reason this matters: a missed backflow testing deadline is not a plumbing problem, it is a letter, and on a commercial connection it can escalate to the water being shut off. Keeping the calendar is cheaper than answering the letter.
Work is carried out by licensed plumbers under our Responsible Master Plumber, license RMP-43333, issued by the Texas State Board of Plumbing Examiners. You can verify that license yourself.
What San Antonio homeowners say
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Frequently asked questions
How often does backflow testing have to be done?
Your water provider sets the interval and annual is the usual answer, with a test also required at installation and after any repair or relocation. We will tell you what your provider requires for your specific assembly.
How long does the backflow testing take?
Fifteen to twenty minutes for a typical residential irrigation assembly. Larger commercial devices and anything in a below-grade vault take longer, mostly because of access rather than the backflow testing itself.
Will my water be shut off?
Briefly, and only downstream of the assembly. On an irrigation system that means the sprinklers rather than the house. On commercial and fire connections we schedule the interruption with you in advance.
What happens if it fails?
It gets repaired, usually with a rebuild kit for that make and model, and then retested. The retest is part of the job rather than a second charge. Where the body is damaged or parts are obsolete, replacement is the honest answer.
Who submits the report?
We do. The report is completed and signed under the tester licence and filed with your water provider, and you get a copy. Chasing paperwork is not something you should have to do.
Why is there water pouring out of my backflow preventer?
If it is a reduced pressure zone assembly, that is the relief valve doing its job — it discharges when an internal check has failed. It means protection has been lost and it needs attention promptly rather than eventually.
Do I need backflow testing on a plain hose bib?
No. A hose bib vacuum breaker is a non-testable device — you replace it rather than test it, and they cost very little. Testable assemblies are the ones on irrigation, pools, boilers, fire lines and commercial connections.
My assembly froze and split. Can it be repaired?
Rarely. A freeze usually cracks the body itself, and a cracked body is a replacement. Draining the assembly before a hard freeze and fitting an insulated cover prevents nearly all of it.
Can any plumber do this?
No. Testing has to be carried out by a licensed backflow prevention assembly tester using a calibrated gauge, and the report is signed under that licence. A provider can reject a report submitted without one.
I bought a house with an irrigation system. Where do I start?
With a test. You inherit the assembly and the obligation, and you will not know what condition it is in or when it was last certified. It is a small job that puts you on a known footing.
Do you test fire sprinkler backflow assemblies?
Yes, and we coordinate the shutdown so the system is not left unprotected longer than the backflow testing requires. Those are scheduled rather than done on a drop-in basis.
Can you handle several properties at once?
Yes. We hold the assembly details for each site and come back on the cycle. Multiple devices tested in one visit are cheaper per device than separate call-outs, and the reports go out together.
Get the backflow testing done and the paperwork filed.
Licensed tester, calibrated gauge, report submitted to your provider, and a repair quote on the spot if it fails.
Silverback Plumbing & Drain provides licensed plumbing and drain service for homes and businesses throughout the San Antonio area. From emergency repairs to routine maintenance, we diagnose the problem, explain the fix, and get it done right the first time.
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Copyright © 2026 Silverback Plumbing and Drain
Mark Vargas, Responsible Master Plumber #43333 Licensed through the Texas Board of Plumbing Examiners P.O. Box 4200, Austin, Texas 78765 (800-845-6584)