Thornton requires annual tests on commercial, multi-family, fire, and irrigation assemblies, filed through BSI Online.
Thornton backflow rules at a glance
| Water provider | City of Thornton, Cross-Connection Control & Backflow Prevention Program |
|---|---|
| Who | Commercial, industrial, and multi-family properties with more than two units |
| How often | At installation and at least once a year. Containment assemblies on main domestic, fire, and irrigation lines must be tested every year; higher-hazard assemblies may need testing twice a year. |
| How reports are filed | Online through BSI Online (Backflow Solutions Inc.), which charges a fee for each report |
| Deadline | Before the annual due date. The city's FAQ says annual tests must be submitted no later than 60 days after the original due date. |
| Failed test | Report it to BSI and email the city within 24 hours. Repairs are due within 30 days, and extensions are possible. |
| If you miss it | Missed deadlines can lead to disconnection of water service. |
| Program contact | 720-977-6586, back.flow@thorntonco.gov |
Summarized from City of Thornton's published program information (source), checked October 2026. The notice from your water provider always has the final word on your due date.
You can hire any certified tester
Thornton doesn't recommend one testing company over another. Any certified backflow tester can test in Thornton, and the report goes through BSI Online either way. Testing itself doesn't need a city permit; a permit is needed when plumbing changes, like installing a new assembly.
Containment vs. isolation
Thornton requires annual tests on containment assemblies, the ones protecting the city's water system at the main domestic, fire, and irrigation connections. Isolation assemblies further inside a building are recommended for annual testing but handled differently. If you're not sure which yours is, we can tell you on site.
What we do on a Thornton backflow test
- Confirm the assembly type, size, and serial number against your provider's records
- Test every check valve and relief valve with a differential pressure gauge calibrated October 2026 and traceable to NIST
- Tag the assembly with the service date, our business information, and the tester's certification number
- File the completed report the way City of Thornton requires
- Send you a copy of the report, with photos
If the assembly fails
Most failures come down to a dirty or worn check valve, a tired relief valve, or a split rubber part. Those get cleaned or rebuilt and retested, usually in the same visit, after you approve the price. If the body itself is cracked, usually from a missed winterization, the assembly has to be replaced. Replacing an assembly is installation work, which in Colorado needs a licensed plumber; we'll tell you exactly what's needed and do the retest once it's in.
Before we come out
- Have the notice from your water provider handy, or send a photo of it when you book
- Tell us where the assembly is, and leave any gate unlocked or the mechanical room open
- For sprinkler assemblies, the water needs to be on. If the system is still winterized, we can do the spring startup and the test in one visit.
Not sure what kind of assembly you have? PVB vs. DCVA vs. RPZ →
Backflow testing nearby
Denver · Aurora · Westminster · Arvada · Northglenn · Broomfield · Golden · Lakewood · Englewood · Commerce City · Wheat Ridge · Parker · Boulder · Louisville · Lafayette · Greenwood Village · Centennial · Commercial & HOA testing · For plumbing & irrigation companies · Every provider's rules
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