Yes, backflow prevention is required by law in Colorado. The Colorado Department of Public Health and Environment’s Regulation 11 — the state’s primary drinking water protection rule — mandates that public water systems require cross-connection control programs, which means requiring backflow prevention devices at connections that pose a contamination risk to the potable water supply. Most water utilities in the Denver metro, including Denver Water, Aurora Water, and others, have their own cross-connection control ordinances that implement and in some cases exceed those state requirements.

What the Law Actually Requires

Colorado’s cross-connection control requirements work on two levels. At the state level, Regulation 11 requires water systems to have a cross-connection control program in place and to enforce it. At the local level, each water utility implements that program through their own ordinances and service agreements.

For most Denver-area homeowners, the most direct legal requirement they encounter is the one tied to their irrigation system. Any residential or commercial irrigation system connected to the public water supply must be protected by an approved backflow prevention assembly — typically a Pressure Vacuum Breaker (PVB) for residential applications, or a Reduced Pressure Zone (RPZ) assembly in higher-hazard commercial settings. The assembly must be installed by a licensed plumber and, once in place, tested annually by a certified backflow tester. Test results must be submitted to the water utility.

Which Properties Are Most Commonly Affected

  • Properties with irrigation systems: Every residential property with an in-ground sprinkler system connected to the public water supply needs a backflow preventer on that connection. This is by far the most common application for Front Range homeowners.
  • Properties with swimming pools or hot tubs: A pool or spa connected to the house water supply for fill or makeup water requires backflow protection at the connection point.
  • Commercial properties: Restaurants, salons, medical facilities, industrial operations, and multi-family buildings often require more robust assemblies — RPZ or double check valve assemblies — depending on the hazard level of the connected use.
  • Properties with boilers or hydronic heating: A heating system that uses chemicals (corrosion inhibitors, antifreeze) in the water and connects back to the potable supply must be protected.

Why Backflow Prevention Exists

The public water supply is pressurized — water flows from the treatment plant to your tap under continuous positive pressure. That pressure is what keeps contaminants from entering the supply line from the outside. But pressure fluctuations happen: a large water main break, peak firefighting demand, or a significant pressure surge can temporarily reverse flow direction in parts of the distribution system.

When that reversal happens, anything connected to the water supply without backflow protection can push its contents backward into the public main. An irrigation system that was just fertilized, a pool that was just shocked with chlorine, or a boiler circuit containing corrosion inhibitors can all become contamination events without proper protection. Backflow preventers use check valves and pressure differentials to physically block that reverse flow regardless of what the system pressure does.

Consequences of Non-Compliance in Colorado

Water utilities have the authority under Colorado law to shut off service to a property that is out of compliance with cross-connection control requirements — and they exercise that authority. If your utility has notified you that a backflow preventer needs to be installed or tested and you haven’t complied by the deadline, service disconnection is a real possibility. Beyond that, if a backflow event occurs from your property and causes contamination, liability exposure is significant.

If you’ve received a notice from your utility or aren’t sure whether your property is compliant, Done! can assess your connections, install the required assembly, and schedule the certified annual testing. Learn more on our pressure and backflow prevention page, or contact our plumbing team to get your property into compliance.