Thornton's backflow test, decoded — who, when, and where it files
If your letter says City of Thornton, here’s the whole shape of the requirement — from the city’s own cross-connections and backflow prevention page, checked July 2026.
The rules in three lines
- Who: commercial, industrial, and non-single-family residences — the city’s definition is any residence greater than two units. The legal basis is City Ordinance 74-156.
- When: a certified Backflow Technician tests each assembly at installation and at least annually after that.
- Where it files: results go online to Backflow Solutions, Inc. (BSI Online) — before the annual due date on your notice.
BSI is the part to get right
Thornton is a BSI Online city — the same portal several Front Range districts use (see how filing differs district by district). The tester submits through BSI; portal filing fees, when they exist, are typically priced into the quote (one of the drivers in what a test costs). The question to ask when booking isn’t “are you certified?” — it’s “do you file with Thornton through BSI, and will it land before my due date?”
Thornton’s page also says something worth respecting: the city doesn’t recommend specific testing companies. Nobody’s on a city list because they paid to be — which means your job is picking a tester who knows this specific program. That’s what the form below reaches.
If the letter confuses you
The notices are written in program language — our letter decoder translates the standard paragraphs. Questions about your specific requirement go to the program itself: back.flow@thorntonco.gov or 720-977-6586.
Questions people actually ask
Who has to test backflow assemblies in Thornton?
Commercial, industrial, and any residence bigger than two units — that's the city's own line. Single-family homes aren't named in the mandate, though an assembly that exists still ought to work. Testing happens at installation and at least annually after, by a certified Backflow Technician.
Where do Thornton test results get filed?
Online through Backflow Solutions, Inc. (BSI Online) — before the annual due date on your notice. The tester files it; your job is confirming they actually did, because an unfiled test doesn't exist as far as the compliance clock knows.
What law requires this in Thornton?
City Ordinance 74-156 requires backflow preventers or cross-connection devices on applicable properties. The program's contact is back.flow@thorntonco.gov or 720-977-6586.
Will the city recommend a tester?
No — Thornton's page says plainly it doesn't recommend specific testing companies over others. That's what the form on this page is for: reach a certified tester who already files with Thornton's BSI account and knows its calendar.