Updated October 28, 2026
A backflow preventer can look perfect and still be broken inside. Its job is to stop dirty water from running backward into the water lines, and the only way to know it still does that is to put a gauge on it. That’s why Virginia makes the owner test it once a year. In Northern Virginia our yearly backflow test is $250, normally $300, and you can book or pay for it on our backflow testing page.
Think of it like a smoke detector. It sits there quietly for months, you never think about it, and the one day it matters is the day it has to work. The test is you pressing the button.
Why backflow testing is required every year in Virginia
It’s state law. Virginia’s waterworks rule, 12VAC5-590-600, says a testable backflow preventer gets tested “after initial installation, immediately after repairs or relocation, and annually thereafter.” The same rule puts that job on the water customer. For a house, that’s the owner, not the water company and not the builder.
Every water supplier around here follows it:
- Loudoun Water wants devices tested every year by a tester who holds the state’s certification.
- Fairfax County gives each property its own testing month, set by where the house sits on the county’s tax map.
- Stafford County tests residential devices at install and every year after, and mails a reminder 30 days before the due date.
- Fauquier County‘s water authority says devices are inspected and tested annually.
So the yearly test isn’t a sales pitch. It’s the rule, and the letter you got is your water supplier keeping track of it. If you’re not sure you even have one, start with what a backflow preventer does.
What wears out inside a backflow preventer in a year
Inside the brass are a few small parts doing a hard job. Spring-loaded check valves, little doors that only swing one way, snap shut whenever water tries to go backward. Rubber seals make those doors watertight. Here’s what goes wrong with them:
- Springs get tired. A weaker spring closes slower and looser.
- Rubber gets stiff or nicked. A seal that used to close flat now lets a trickle by.
- Grit gets stuck. A tiny bit of sand or rust can prop a door open.
You can’t see any of that from outside. Water still comes out of every faucet, the lawn still gets watered, and nothing drips. The device fails quietly, which is exactly why somebody has to check it with a gauge.
Local rules expect the rubber to wear out on a schedule. Purcellville and Middleburg both say most devices need an overhaul every five years to replace the rubber parts, and Manassas requires that overhaul every five years on top of the yearly test.
$250 Yearly Backflow Test
The yearly test your water utility or county asks for, on a home's backflow preventer up to 1 inch. About backflow testing
Why winter makes the yearly backflow test matter more
Most backflow preventers on houses here sit outside, on the lawn sprinkler line, sticking up from the ground. Water left inside one in a hard freeze turns to ice, ice takes up more room than water, and the brass body or the parts inside crack. A freeze-cracked outdoor device, a pressure vacuum breaker or PVB, is the failure our plumbers see most.
That’s why fall winterizing matters, and why the spring test matters too. Loudoun Water says a device taken off for winter gets retested once it goes back on. A crack can be hair-thin and still let the device fail.
If yours is already dripping or spraying, read what a leaking backflow preventer means and what a broken backflow preventer looks like.
What the yearly backflow test protects you from
The test isn’t really about the brass. It’s about what’s on the other side of it.
Your lawn sprinkler pipes sit in soil that gets fertilizer and weed killer. Loudoun Water warns that sprinkler water can become contaminated from lawn care chemicals and can get siphoned back through the sprinkler heads. If the water main breaks or a crew flushes a hydrant, pressure in the street drops, and a bad backflow preventer lets that sprinkler water get sucked back toward your kitchen tap. Prince William County says the device is there so fertilizers do not enter the water in the house.
That pressure drop is the whole story behind backflow, and we explain it simply in backflow and water pressure. For the bigger picture: what backflow is in plumbing and the signs of a backflow problem.
Who is allowed to do the yearly backflow test
Not just anybody with a gauge. Since January 1, 2023, Loudoun Water treats a report as void if the tester doesn’t hold the state’s backflow certification from DPOR, Virginia’s licensing board. Prince William Water says devices are tested by a backflow testing company that holds that certification, and its form is filled out by the tester who did the test.
The owner is still the one on the hook for the report reaching the water supplier, so it pays to use someone who sends it for you and tells you when it’s in.
When your yearly backflow test is due
Your water supplier tells you. Most send a letter or email with a due date, and the due date comes back around every year.
- Fairfax County: your month is set by your tax map grid, and the report is due within 10 business days of the test.
- Loudoun Water: a device that fails has 30 days to be fixed and retested.
- Stafford County: the tester should get the report in within 7 days.
Find your area: Fairfax County, Loudoun County, Prince William County, or towns like McLean, Centreville, Purcellville, Middleburg and Manassas. Live in a neighborhood with an HOA? Here’s how HOA backflow testing works. And here’s what happens if you skip a backflow test.
What happens at the yearly backflow test
It’s short. A plumber closes the shutoff valves, hooks a gauge to the little test cocks on top, and checks each one-way door and the relief valve or air inlet. Pass, and it gets a tag and a report. Fail, and you find out exactly which part let go.
Every step: what happens during a backflow test. Test or inspection? Here is the difference. And the full price breakdown: what a backflow test costs.
Why SwiftPro makes the yearly backflow test easy
Once a year shouldn’t mean a week of phone tag. Here’s how it goes with us:
- Pay $250 online, normally $300. Or call (703) 997-9757, or book a time online, whichever you like.
- We call you to pick the day. Tell us where the device is and whether the sprinkler is shut down for winter, and keep your notice handy.
- We test it and tag it. A SwiftPro plumber hooks the gauge to the device, reads every check and writes the numbers down.
- We send the report where your water supplier wants it. Loudoun Water, Fairfax County, Prince William Water and the town programs each take it their own way, and yours goes in the way your notice asks.
- If it fails, you get a written quote before any repair. Nothing gets fixed until you say yes, and the device is tested again once it is.
Set it and forget it until next year’s letter. Everything is on our backflow testing page.
Yearly backflow test questions
Why do I need a backflow test every year?
Because the springs and rubber inside wear out and freezes crack the body, and none of it shows from outside. Virginia’s waterworks rule says testable devices are tested after install, after repairs and every year after.
Is the yearly backflow test required by law?
Yes. Virginia rule 12VAC5-590-600 requires the yearly test and puts it on the water customer, which for a house is the owner. Your water supplier enforces it.
When is my backflow test due?
Your water supplier’s letter or email gives the date. In Fairfax County each property has its own testing month, set by the tax map grid.
Do I need a backflow test after winter?
If the device was taken off or drained for winter, yes. Loudoun Water retests a device after it’s reinstalled, and a freeze crack can make a device fail even when it looks fine.
Can I skip a year if my backflow preventer passed last time?
No. A device that passed last spring can fail this spring, which is the whole reason the rule says every year.
How long does a yearly backflow test take?
A device that passes is a short visit: shut it off, read the gauge, tag it. A failed device takes longer, and you get a written quote before any repair.
How much is the yearly backflow test?
$250 for one home, normally $300, on a residential device up to 1 inch. You can pay online and we call to pick the day.
Book this year’s backflow test
Call (703) 997-9757, book online, use the form at the top of this page, or pay $250 online and we’ll call to pick the day. Everything about the test is on our backflow testing page, and current deals are on our offers page.
SwiftPro Heating, Cooling & Plumbing tests, repairs and replaces backflow preventers, water heaters, sump pumps and water and drain pipes, and services furnaces, heat pumps and air conditioners, across Northern Virginia from Chantilly and Ashburn, with a separate plumbing team and a dedicated HVAC team. Family owned, BBB Accredited with an A rating, 24/7 emergency service, Virginia Class A contractor license 2705192276, and rated 5.0 stars across 1,130 reviews on Google, Angi, Yelp, the BBB and Facebook. Read the reviews.
