The world of water safety, piping infrastructure, and regulatory compliance can quickly become complex. Among myriad definitions, standards, and backflow prevention methods, devices, and assemblies, critical work is happening. Gaining a more robust understanding of what “backflow prevention” and “cross-connection control” practically mean can help you better protect your community, your employees, your residents, or your patients.
Key Definitions
Backpressure vs. Backsiphonage
Let’s start with the basics. What is backflow and how does it occur?
Backflow is the reversal of the normal flow of water in a piping system. There are two causes of backflow: backpressure and backsiphonage.
Backpressure occurs when the downstream pressure exceeds the supply pressure. Backpressure can occur in pressure-producing and elevated systems—think HVAC systems or boilers. If the system malfunctions and fails to create the pressure necessary to maintain the normal flow of water, backflow can occur.
Backsiphonage occurs when a vacuum or partial vacuum is created that induces a flow in the opposite direction. Backsiphonage is commonly caused by an interruption to the water supply—think fire hydrant usage or a water main break. With the introduction of significant outside pressure, a vacuum is created, reversing the flow of water.
Cross-Connections & Getting Them Under Control
A cross-connection occurs when the potable water supply is connected—either by accident or by design within the piping system—to a non-potable line. Where cross-connections exist, the risk of contamination exists. In residential buildings, the most common cross-connection is the simple garden hose. Industrial and healthcare facilities face unique challenges in controlling cross-connections due to size, complexity, and a variety of interior connections. Plumbing codes require all cross-connections to be isolated from the potable water supply by the appropriate form of backflow prevention.
Cross-connection control is the process of eliminating or protecting each cross-connection in a building or water supply system. Most states require dedicated programs and monitored efforts to cover all cross-connection control activities within public water systems, including requirements for all buildings in a community—residential, commercial, and industrial. These programs can include on-site surveys to detect unsafe conditions, backflow prevention assembly test tracking, and compliance enforcement.
The Basics of Backflow Prevention
Backflow prevention is split into three groups: methods, devices, and assemblies.
The backflow prevention method is simply an air gap—a vertical distance between the supply pipe and the flood level rim. Typically, requirements dictate that the air gap must be a minimum of one inch.
Backflow prevention devices are simple mechanisms that do not require periodic testing. The most common backflow prevention devices include atmospheric vacuum breakers and dual check valves. These devices are used on both high- and low-hazard connections with strict adherence to proper installation and limitations based on application.
Note: While devices may not be testable, that does not mean they should not be inspected for compliant installation and application, and any indications of malfunction.
Backflow prevention assemblies are complicated mechanisms that typically require periodic—often annual—tests performed by qualified technicians. The most common assemblies include double check valve assemblies and reduced pressure zone (RPZ) assemblies. Double check valve assemblies are used for low-hazard connections, while RPZ assemblies are mandatory for high-hazard connections where backpressure can occur.
Degrees of hazard depend on the substance at risk of entering the water supply. Pollutants are low hazard and considered non-toxic: The potable water supply may suffer an aesthetic change impacting the appearance, smell, or taste of the water, but pollutants do not present a serious health risk to consumers. Contaminants are high hazard and considered toxic: Contaminated water presents a risk of serious injury or death to consumers.
Identifying Backflow Preventers
Backflow prevention devices and assemblies are approved and standardized by the American Society of Sanitary Engineering (ASSE). Most plumbing codes recognize and reference the ASSE Standards for backflow preventers and other plumbing devices. On each preventer, look for the four-digit number that indicates what type it is. For example, a hose bibb vacuum breaker’s referenceable ASSE number is 1011, typically stamped right on the device.
Why It Matters: Cases of Cross-Connections
Cross-connections and backflow are responsible for a significant portion of waterborne disease outbreaks in the United States. Examples of these crises abound:
- In 2016, a backflow incident in Corpus Christi, Texas, left residents unable to use their tap water for four days.
- In 2018, a contamination event in Delray Beach, Florida, resulted in reclaimed water dispensing from the taps of water customers.
- In 2021, a construction company in Gulf Breeze, Florida, mistakenly connected a sewer line to the water main, resulting in sewage-contaminated water running through more than 300 homes.
- In 2022, drinking water at an elementary school in Carlsbad, California, was contaminated after they suffered a cross-connection between recycled water and their potable water system.
- In 2024, residents in West Springfield, Massachusetts, discovered an “oil-like” substance in their water supply due to an unprotected cross-connection between a private plumbing system and the municipal supply.
Public health and safety hinges on access to potable water—in hospitals, schools, businesses, and homes. Understanding the basics of backflow prevention and cross-connection control can help prevent contamination and protect the water supply of community members.
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