When Is Backflow Testing Required in St. Louis?

If you own or manage a commercial building in the St. Louis area, you have almost certainly received a letter asking for a backflow test report. Those letters are easy to set aside, but a missed test can end with a water shutoff notice. Here is a plain-language look at when backflow testing is required, who asks for it, and how to stay ahead of the deadline.

What a backflow preventer does

A backflow preventer is a valve assembly that keeps water from flowing backward out of your building and into the public water supply. Pressure drops happen more often than people think — a water main break down the street, a fire hydrant being flushed, or a large pump starting up can pull water in the wrong direction. Without a working assembly, water from boilers, irrigation, chemical feeds, or process equipment can be drawn into the drinking water that serves your neighbors.

Who requires the test

In Missouri, the rules come from the state's public drinking water regulations, and they are enforced by your local water supplier. Depending on where your building sits, that could be the City of St. Louis Water Division, Missouri American Water, a public water supply district in St. Charles County, or a city-run utility such as O'Fallon or Wentzville. Local plumbing codes adopted by cities and counties add their own installation and inspection requirements. The supplier that sends your reminder letter is usually the one that needs your test report.

How often testing is due

Most commercial backflow assemblies must be tested at least once a year. Testing is also typically required when an assembly is first installed, after it has been repaired, and after it has been moved. Some high-hazard sites may be asked to test more often. Always go by the date on your supplier's notice — due dates can differ from one assembly to the next in the same building.

Which buildings usually need it

• Buildings with a fire sprinkler system tied to the domestic water service
• Restaurants, commercial kitchens, and food processing plants
• Medical and dental offices, labs, and clinics
• Industrial and manufacturing facilities with dedicated water lines or chemical feeds
• Properties with lawn irrigation systems
• Buildings with boilers, cooling towers, or water treatment equipment

Who can perform the test

The test must be done by a certified backflow prevention assembly tester using calibrated test equipment. The tester checks that each check valve holds and that relief valves open at the correct pressure, then files a report with your water supplier. If an assembly fails, it will need repair or replacement and a retest before the report is accepted.

What happens if you miss it

Suppliers usually send a reminder, then a final notice. If a report still isn't on file, the supplier can shut off water service to the building until the assembly passes. For an occupied office, school, or restaurant, that is a very expensive way to find out the test was overdue.

How to stay ahead of the deadline

Keep a list of every assembly in the building, its location, size, and serial number, plus the month it was last tested. Schedule the test a few weeks before it is due so there is time to repair a failed assembly. If you manage several properties, ask your plumbing contractor to track the dates for you.

Legacy Plumbing tests, repairs, and replaces commercial backflow assemblies across the St. Louis metro and files the paperwork with your water supplier. Sign up for an annual reminder on our backflow page, or request service to schedule your test.