A backflow preventer is a plumbing device that stops contaminated water from flowing backward into your clean water supply. Under normal conditions, water pressure keeps water moving in one direction — from the supply into your home. But pressure drops caused by water main breaks, heavy demand events, or firefighting activity can reverse that flow, pulling water from irrigation systems, garden hoses, or other connections back into the potable supply. A backflow preventer stops that from happening.

Why Backflow Is a Real Risk

The municipal water system experiences pressure fluctuations regularly — main repairs, burst pipes, or a sudden surge in fire hydrant use can temporarily drop pressure enough to create a siphoning effect. When that happens, anything connected to your water supply can potentially pull its contents backward into the potable supply.

The most common residential backflow hazards include lawn irrigation systems, which can draw in fertilizer, pesticides, or contaminated soil water; garden hose connections left submerged in buckets or pools; and appliances like boilers or hydronic heating systems that use treated water that should not re-enter the drinking supply. In Colorado, where lawn irrigation is common and in-ground sprinkler systems are standard in many neighborhoods, backflow protection at the irrigation connection is particularly important.

Types of Backflow Preventers

Different applications call for different devices. A pressure vacuum breaker (PVB) is the most common type used on residential irrigation systems — installed above ground at the point where the irrigation line branches off the supply, it prevents back-siphonage by venting to atmosphere when pressure drops. PVBs are required by Colorado plumbing code for most residential irrigation connections.

A reduced pressure zone (RPZ) device provides a higher level of protection and is used where back-pressure contamination risk is greater — hydronic heating systems, commercial applications, or connections where both back-pressure and back-siphonage are concerns. Double-check valve assemblies are a simpler option for lower-hazard connections.

Colorado Code Requirements

Colorado’s plumbing code requires backflow protection at any connection that poses a cross-connection hazard — including irrigation systems, boilers, and certain appliances. Many municipalities in the Denver metro actively enforce this, and some require annual testing of certain backflow prevention devices by a certified tester. If your home has an irrigation system and no visible backflow preventer on the irrigation supply line, it is likely out of compliance and your water utility could require installation.

  • Pressure vacuum breaker (PVB) — required on most residential irrigation systems in Colorado
  • Reduced pressure zone (RPZ) device — higher protection for boilers and hydronic systems
  • Double-check valve assembly — lower-hazard applications
  • Annual testing required for testable devices by a certified backflow tester
  • Freeze protection critical in Colorado — PVBs must be winterized before hard freezes

Maintenance and Annual Testing

Testable backflow preventers — primarily RPZ devices and some double-check assemblies — must be tested annually by a certified backflow tester and results reported to the local water authority. PVBs used on irrigation systems should be inspected each spring when the irrigation system is reactivated. Freezing is a major concern in Colorado: a PVB left in service through a hard freeze will crack and fail, leaving the system unprotected and potentially leaking.

A backflow preventer that looks intact externally may not be functioning correctly internally — seals and check valves wear over time, and a failed device provides no protection. Annual testing is how you confirm the device is actually doing its job.

If you’re not sure whether your home has the right backflow protection in place — or whether your existing device has been tested recently — Done can inspect and evaluate your setup. Learn more on our pressure and backflow prevention page, or visit our plumbing services page for the full range of residential plumbing work we handle.