What backflow is and why your utility wants a test

What backflow is

EPA Cross-Connection Control Manual (Feb 2003) model ordinance defines backflow as flow under positive or reduced pressure in the distribution pipes of a potable supply from a source other than its intended source.

A backflow preventer is a device or means designed to prevent backflow or backsiphonage (EPA manual model ordinance).

A backflow preventer is a device installed in a water line that stops water or other substances flowing backward into the water supply (City of Manhattan, Kansas utility document).

Backsiphonage is backflow caused by reduced system pressure that creates sub-atmospheric pressure in the water system (USC Foundation).

Backpressure is downstream pressure (pump, elevated piping, steam or air pressure) above the supply pressure that tends to reverse flow (USC Foundation).

Backsiphonage can occur when distribution system pressure falls below plumbing system pressure, for example when a fire truck draws water or a main breaks; Arkansas Department of Health consumer overview.

Backpressure occurs when pressure in a private system exceeds public distribution pressure, so normal flow reverses.

Sources: Backflow defined (USC Foundation); Backflow defined (EPA manual model ordinance); Backflow preventer in plain terms; Backsiphonage cause (Arkansas Department of Health); Backpressure cause (City of Boulder)

Cross-connections

Cross-connections are the links through which contaminating materials can enter a potable water supply.

EPA states cross-connections between potable and nonpotable supplies constitute a serious public health hazard.

EPA Distribution System Toolbox fact sheet (Dec 2021) defines cross-connections and backflow and links backflow to serious public health hazard.

EPA names private irrigation systems and fire sprinkler systems as common cross-connection points with public water.

EPA cites a 2010 Water Research Foundation study using backflow-detecting meters: 5 percent of homes registered a backflow incident of 1 gallon or more each year.

Any actual or potential connection between the public drinking water system and another system that could introduce a contaminant counts, and can affect public health.

Cross-connections exist wherever the water supply connects to equipment that can act as a source of pollution or contamination.

City of Manhattan, Kansas calls outdoor hose bibbs (sillcocks) the largest single source of cross-connections; a hose in a bucket creates one.

Sources: What a cross-connection is (EPA manual); Cross-connection and backflow in EPA fact sheet; Cross-connection defined (City of Boulder); Cross-connection sources named by a utility

Why tests are yearly

Preventers are mechanical with springs, moving parts and rubber seats that wear, so they must be tested and maintained.

Manhattan: preventers must be properly tested and maintained to keep the water supply safe.

EPA: test cocks let a double check be tested to find whether either check valve is inoperative or fouled by debris.

Oregon state law and Portland City Code require backflow prevention assemblies to be tested at least once each year.

Portland: owners can be held liable for illness or injury if a failed assembly is not promptly repaired.

Portland tells residential customers to test each spring because most residential assemblies are on irrigation systems.

Boulder says assembly tests are required annually per state regulations.

CSU Extension: devices must be certified upon installation and at least annually to ensure continued backflow prevention.

Sources: Why backflow preventers wear out (City of Manhattan); Testable double check can show which check is fouled (EPA manual); Portland and Oregon require a test at least once each year; Annual tests required per Colorado regulations (City of Boulder); Certified at install and at least annually (Colorado State Univ. Extension)