Updated November 2, 2026
Two ways water runs backward
- Backpressure: the building side pushes harder than the main. Pumps, boilers and a water heater's thermal expansion can do it.
- Backsiphonage: the main loses pressure, after a main break or heavy hydrant use, and pulls water back out of the building.
Who needs one
The hazard decides. Typical triggers are equipment that can push or hold contaminated water against the supply: treated boiler feeds, chemical dispensers and carbonated beverage equipment in kitchens, irrigation, laboratory and medical equipment.
DEP keeps the list of property types that must have a device. For a specific property, a Professional Engineer (PE) or Registered Architect (RA) makes the call with DEP's Backflow Prevention Risk Assessment Guide. A property with more than one water service needs a device on each.
RPZ or double check
The containment device sits on the service after the meter, ahead of the first branch, so the whole building is separated from the main.
| Device | Hazard | What to know |
|---|---|---|
| Reduced pressure zone assembly (RPZ) | High or low | A relief valve dumps water when a check fails, so it needs an air gap and a drain sized for full discharge. |
| Double check valve assembly (DCVA) | Low | No relief discharge. |
| Vacuum breakers | High or low, backsiphonage only | For single fixtures and hose connections. DEP does not accept them as the main (containment) device. |
Installing a new device, step by step
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Survey
What the water feeds, how many services, the size of each, what is installed now.
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Plan
A PE or RA prepares the backflow prevention plan and sends it to DEP. For double check assemblies, DEP lets the PE or RA self-certify the plan.
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Approval
DEP mails the approval.
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Installation
DEP requires a Licensed Master Plumber to install the device.
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Initial test
A tester certified by the New York State Department of Health tests the device. The form is signed by the tester, the Licensed Master Plumber and the PE or RA who filed the plan, and goes to DEP within 30 days of installation. DEP takes the form online, with the signed and sealed form attached.
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Every 12 months
The same test by a certified tester, the form signed by the tester and a Licensed Master Plumber, filed with DEP. DEP mails a reminder when the test is due and offers email reminders.
If a DEP letter arrived
DEP puts installation and upkeep on the property owner, not on tenants.
- An order to install. DEP gives a 30-day installation period. If the work is under way, DEP accepts written certification from a Licensed Master Plumber, PE or RA that the device is being installed.
- A reminder that the yearly test is due. Book the test before the date on the letter. DEP can fine the owner or shut off the water service when a test is missed.
- DEP has no record of a device that is there. The PE or RA who designed it sends DEP a record drawing and an initial test report.
What decides whether a device passes
- Access. Test cocks reachable without a ladder; the device protected from freezing, flooding and damage.
- Clean water. The line is flushed before the device goes in. On new installations, most failed tests are debris in a check valve or the relief valve.
- Drainage. The RPZ relief discharges through an air gap to a drain that can take full flow.
- Thermal expansion. A device closes the system, so a storage water heater downstream needs an expansion tank on its cold supply (NYC Plumbing Code 607.3).
- Shutdowns. The test closes the device's outlet valve, so water to the building stops for the length of the test. Where water cannot stop, two devices in parallel.
How PlumbHub handles it
We coordinate the sequence from the survey to the yearly test: the plan, the installation, the initial test and each yearly test, with every DEP form signed by the people DEP requires. You keep a copy of each test report.
PlumbHub LLC is a plumbing project contractor. Permitted plumbing work in New York City is filed, supervised and signed off by the New York City Licensed Master Plumber engaged for each project.
Questions
How often does a backflow preventer need testing in NYC?
Every 12 months after the initial test, by a New York State-certified tester. The report goes to DEP.
Who signs the test form?
For the initial test: the certified tester, a Licensed Master Plumber and the PE or RA who filed the plan. For the yearly test: the certified tester and a Licensed Master Plumber.
The device failed its test. Does it have to be replaced?
Not always. Most failures are a fouled check or relief valve, and the manufacturer's repair kit fixes many of them. The device is retested after the repair.
Does a tenant have to arrange the test?
No. DEP puts installation and upkeep on the property owner.
The building has two water services. Is one device enough?
No. Each service line needs its own device.