What interview questions should you ask a backflow tester? (with good answers)
A question bank for employers: technical questions with the answers to listen for, customer and behavioural questions, a practical task, red flags and a scoring method.
The best backflow tester interview questions come in three groups: technical questions with right answers — assembly types, test procedures, credentials — then customer and behavioural questions where you are listening for judgment, then a practical task the candidate performs in front of you.
Below is the bank for each group, with what a competent tester should say, the answers that are red flags, and a simple way to score candidates against each other.
Before the interview
Write the questions before the candidate is in the room — and write them from your own posting.
The duties you listed are the test blueprint: decide first what you are actually hiring this person to do, because the trade splits.
ASSE's backflow series includes a standard for each of these roles — the 5110 Backflow Prevention Assembly Tester, the 5120 Cross-Connection Control Surveyor, the 5130 Backflow Prevention Assembly Repairer, the 5140 Fire Sprinkler Cross-Connection Control Tester and the 5150 Backflow Prevention Program Administrator — and a shop that needs a surveyor is asking different questions from one that needs a pair of hands on a test kit.
Before an offer you may ask about an applicant's skills, education, work history and required certifications and licences, and you may ask them to describe or demonstrate how they would do the job's tasks — that is what the practical section below is for.
State the job's physical requirements and ask whether the candidate can meet them.
The EEOC's own examples are lifting a certain amount of weight and climbing ladders; whatever your routes actually hold — the lifting, the ladders, the access — say what the job demands and ask directly whether the candidate can do it.
Know what you may not ask before an offer.
Not about past job injuries or workers' compensation history — keep "ever hurt your back on the job?" off the sheet, out of the phone screen and out of small talk.
You may ask about current illegal drug use, but not about lawful prescription medication.
And salary-history questions are banned in Virginia, Hawaii, Rhode Island, D.C. and California — the jurisdictions this research verified, plus others it did not check — so treat that as a floor rather than the full map.
The safe habit everywhere: post the pay range and ask what the candidate is looking for.
Which of these rules binds you depends partly on your size.
Federal EEO laws — Title VII and the ADA — cover private employers with 15 or more employees; the age discrimination law covers those with 20 or more; the Equal Pay Act covers virtually all employers.
A shop with 4 to 14 employees is still covered by the Immigration Reform and Control Act's national-origin and citizenship discrimination rules, which the U.S. Department of Justice enforces.
Your state's rules may cover smaller employers than the federal ones — check them too.
Run the same questions, in the same order, for every candidate.
You will compare answers fairly, and your notes will still make sense by the time the last interview of the week is done.
The full sequence — sourcing, credential checks, pay, onboarding — is our guide to how to hire a backflow tester; this page picks up at the interview itself.
Which technical questions test real backflow tester skill, and what are good answers?
Walk me through a backflow assembly test, start to finish — from arriving at the building to the report.
What to listen for: A sequence, not a highlight reel: the assembly isolated from the supply, the test kit set up deliberately rather than from habit, the readings taken in the order the test procedure requires, the assembly and the line restored, the result recorded.
Backflow testing is procedure-driven work — ASSE, the publisher of the 5110 tester standard, tests to multiple field test procedures, including the USC 10th Edition procedure, and some jurisdictions require a specific one — so a working tester narrates the steps they hold themselves to and names the procedure they follow, not just the outcome.
A story with no isolation step and no restoration step is a memory, not a test.
Which assembly types can you test, and how do you prove it?
What to listen for: The four types the ASSE 5110 practical exam puts candidates on — the RP, the double check valve assembly, the PVB and the SVB — named without looking anything up, and then the proof: a current certificate or licence they can produce, not a card photo.
The ASSE standard's own entry route is at least five years of documented related field experience, a 40-hour training course, a written exam and that hands-on practical, so a tester who passed it has been through that practical and can tell you what it put them through.
What you don't need is a lecture on how each device works from memory — you need the types they are actually qualified on and the document that shows it.
You've tested in two towns with different water purveyors. What changed between them?
What to listen for: Listen for the paperwork and the procedure: which field test procedure the jurisdiction required, which report form, and who the test went to.
The USC Foundation for Cross-Connection Control and Hydraulic Research publishes the Tenth Edition Manual, and its Tester Training Course combines lectures with hands-on wet-lab exercises — a tester trained that way knows the procedure is written down somewhere and finds it before the first test rather than after the first callback.
A candidate who says “the testing was the same everywhere” is telling you they test from habit, and habit is what fails when the next jurisdiction wants a different procedure.
Your test kit — who checks it, and how do you know it's still credible?
What to listen for: An answer with a record in it: where the kit's calibration status is tracked and what they do when the gauge is due.
Annual testing and annual gauge calibration are the common local rules our research found, though it did not verify them from a primary source — the schedule belongs to your water purveyor or your code, so ask the candidate how they track it rather than what the interval is.
Expect them to know the schedule is somebody's rule and that the record lives in writing.
“The kit just works” is the answer that hands you a disputed test with no way to defend it.
Where you've worked, what credential covered the backflow testing — and what could you test under it?
What to listen for: The credential and the issuer, named cold — and, just as telling, whether they know the answer changes by place.
Our research found state-issued tester credentials in Texas, where a TCEQ Backflow Prevention Assembly Tester licence is required of anyone who tests or repairs backflow prevention assemblies; Arkansas (Assembly Testing Technician); Virginia (backflow prevention device worker); Wisconsin (Cross Connection Control Assembly Tester); Minnesota, where the tester needs current ASSE 5110 certification; and Washington, where the plumber PL30 specialty requires a state DOH Backflow Assembly Tester certificate.
Louisiana and Texas also offer a plumber Water Supply Protection Specialist endorsement.
ASSE counts more than 19,000 certified backflow professionals across all 50 states — but which document your jobs require is set by your jurisdiction, so confirm with the issuing body, or the city or county where requirements are local, and verify every credential through the issuer's own record, never a photo of a card.
When did your certification last renew, and what did the renewal involve?
What to listen for: A date they know without checking their wallet: ASSE certifications renew every three years, and recertifying up to six months early loses no time — the 5110 recertification is at least an 8-hour class, a 50-question written exam (rising to 100 questions from January 1, 2027) and a hands-on practical.
A tester who lets the credential lapse doesn't just risk their own work — they can idle the retests your purveyor-bound paperwork is waiting on, so the currency of the card is a scheduling question for you, not a formality for them.
Which customer and behavioural questions matter most?
Your test needs the water off while you run it, and the manager on site is furious about the shutdown. What do you do?
What to listen for: The shutdown explained before it starts — why the test is required and who requires it — and the water restored the moment the test is done, not after lunch.
A tester works in occupied buildings where the customer experiences the test as a disruption; listen for whether they set expectations before the shutoff instead of apologising after, and whether they know when to reschedule rather than argue.
The tester who shrugs “it only takes a few minutes” while the manager watches a kitchen stand still is generating your next complaint call.
You fail an assembly and the owner says it tested fine last year — then asks you to just pass it this time. What happens?
What to listen for: No hesitation: the result is what the gauge says, the failure gets reported, and the owner gets the finding in writing with what happens next — repair or replacement, then a retest.
You are listening for the line they will not cross even for a customer they like, because your name goes on every test report they file.
A candidate who narrates how they once smoothed a failure over “just to be helpful” is telling you, cheerfully, that your liability is negotiable.
Tell me about the angriest customer or building manager you've ever had to deal with.
What to listen for: A specific story, told calmly: what set it off, what the candidate did, how it ended.
You want de-escalation and documentation, not victory.
A candidate who tells every story as “the customer was unreasonable” will recreate that conversation on your next commercial account.
Tell me about an assembly that failed and what you did about it.
What to listen for: A real failure, with the sequence after it: the finding explained to the customer, the repair or replacement handled by whoever was qualified to do that work, the retest, the paperwork that closed it out.
A tester with years in the field should have failure stories, and the fix story is where their judgment lives.
“That's never happened to me” from a candidate with years in the field is not a flex — it is a memory problem.
Why did you leave your last contractor, and what would the owner say about your work?
What to listen for: A checkable answer: names, the kind of work they ran, a reason you can confirm on a reference call.
Vague on names usually means vague on history.
Ask what their boss would call their weakness — then actually call and compare.
What practical task should a backflow tester candidate do?
At the bench: here's an assembly and a test kit — connect the kit and run the test in front of us, narrating as you go.
What to listen for: The setup in the order the test procedure requires, the kit checked before any reading is taken, and readings read off the gauge rather than announced from expectation — then the assembly and the line restored before they call it done.
You are watching whether the hands match the interview: a tester who narrates each step unprompted has run this test on working jobs, and one who falls silent and improvises has watched it.
We've seeded a fault on this mock-up assembly — find it.
What to listen for: The order of the checks, not the speed: what they rule out first, what reading changes their mind, and whether they can say “I need to open this to confirm” instead of pointing and guessing.
A guess on a real job becomes a passed assembly that isn't passing anything.
Fill out the test report for the test you just ran — this is the form we use.
What to listen for: Every field completed from the readings in front of them, not from memory afterwards — and a question back when the form isn't the one they know, asking which report your water purveyor or program requires.
The report is the deliverable the whole job exists to produce; a tester who treats it as an afterthought will hand you paperwork that bounces when your customers' purveyor reviews it.
Here are photos of five devices — name each one.
What to listen for: The four assembly types from the ASSE 5110 practical — RP, double check valve assembly, PVB, SVB — named without hedging.
The fifth photo is none of them, and the answer you want there is “not one of the four” — not a guess at what it is.
The “I don't know, I'd want to see it in person” on anything outside their experience is a good answer, not a weak one.
Which answers are red flags?
None of these is automatically a no — but each should stop the interview long enough to verify, and a couple should end it.
- A spotless record. Every assembly passed, nothing ever failed, no test ever bounced. A working tester should have failure stories — the candidates you can trust are the ones who can tell you one and what it changed.
- The unnameable credential. They claim certification or a licence but cannot say which document or who issued it. Which credential a job requires is set by the jurisdiction — a state licence in one place, an endorsement in another — so a claim that cannot be named cannot be checked through the issuer's record before you offer.
- The kit just works. No idea when the test kit was last checked, no record, and a shrug about where such a thing would live. Whatever your water purveyor requires of the kit, an untracked kit is your liability the first time a test result is disputed.
- No procedure anywhere. They test “however the last town wanted” and cannot name the procedure they follow. Some jurisdictions require a specific procedure, and a tester with none in the answer is one you will be re-teaching on every new account.
- 'Just pass it' stories. Any story where an assembly got signed off with a known problem — to save a customer, to save the schedule, because the purveyor “never checked.” This one should end the interview.
- Guess-first diagnosis. Fault stories end with “so I replaced it and it passed” with no isolation step in between. On a device whose whole purpose is protecting drinking water, a guess is not a callback — it is a finding with your company's name on it.
- The inspector joke. Brags that the purveyor's reviewer “just stamps them” or that reports never get looked at closely. However meant, it tells you how the paperwork on your tickets gets done.
- Every past employer is a villain. One bad shop is a story; a row of them is a pattern. Ask what each owner would say, then call and compare.
After the interview
Score the same day, on the same sheet.
Four rows — technical answers, customer answers, the practical task, credentials — each rated one to five, with a line of notes on the strongest and weakest answer.
Score before the next candidate sits down: memory grades on charm.
Ask every candidate the same questions in the same order.
That is what makes the scores comparable — and consistent questions and a written scoring sheet also give you a record of how each candidate was judged.
Under the Uniform Guidelines on Employee Selection Procedures, a hiring test that has adverse impact on a race, sex or ethnic group is treated as discriminatory unless it has been validated.
If you take candidates onto real work before you decide — a paid working interview for HVAC and plumbing candidates — or you score applicants on a written test, an off-the-shelf HVAC technician skills test included, have an employment attorney review how you run it.
Weight the rows for your work.
A shop whose testing lives or dies on purveyor-bound paperwork leans on the documentation, procedure and credential answers; a shop that sells repair alongside testing leans on the failure stories and the hands-on tasks.
Same sheet, different weights — just decide the weights before the first interview, not after the first offer.
Verify through the source before you offer.
Whichever document the candidate names — an ASSE certification, a state licence, a purveyor-issued certificate — confirm it through the issuer itself; our guide to verifying licences covers the lookup step.
And keep the order of the legal sequence straight: after a conditional offer, you may ask disability-related questions and require medical exams, as long as you do it for all entering employees in that job category.
If your background check comes from a screening company, the Fair Credit Reporting Act's notice and adverse-action steps apply — and the EEOC separately expects a targeted criminal-record screen that considers at least the nature of the offense, the time elapsed and the nature of the job.
When the sheet says yes, browse current backflow tester jobs to see what candidates see on the board.
This page is employer career information, not legal advice. Federal interview rules are enforced by the U.S. Equal Employment Opportunity Commission, and, for smaller employers (4 to 14 employees), national-origin and citizenship discrimination by the U.S. Department of Justice; state and local laws often add rules and reach smaller employers. Confirm what applies to your company with the agencies for your state and an employment attorney.
More hiring resources
Interviewing backflow testers? Post the opening too.
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