Backflow Prevention & Cross-Connection Control Glossary

Understanding the terminology used in backflow prevention and cross-connection control is essential for property owners, plumbers, and facility managers. This comprehensive glossary provides clear definitions of key terms used in the industry.

Air Gap

An air gap is a physical separation between the free-flowing discharge end of a potable water supply and an open or non-pressure receiving vessel. This vertical distance must be at least twice the diameter of the supply pipe and never less than 25mm (1 inch). Air gaps provide the highest level of protection against backflow and are considered the only fail-safe method of preventing backflow.

Approved Backflow Preventer

An approved backflow preventer is a device that has been tested and certified by a recognized testing organization such as CSA (Canadian Standards Association), ASSE (American Society of Sanitary Engineering), or AWWA (American Water Works Association). These devices must meet specific performance standards and be approved for use by the local water authority.

Atmospheric Vacuum Breaker (AVB)

An atmospheric vacuum breaker is a backflow prevention device consisting of a check valve member and an atmospheric vent. It prevents back-siphonage only and must be installed at least 150mm (6 inches) above the highest point of water use. AVBs cannot be used under continuous pressure and are commonly found on irrigation systems and laboratory equipment.

Back Pressure

Back pressure occurs when the pressure in a non-potable system exceeds the pressure in the potable water supply system. This can force contaminated water to flow backward into the clean water supply. Common causes include pumps, boilers, elevated tanks, and thermal expansion in closed systems.

Back Siphonage

Back siphonage is a form of backflow caused by negative pressure (vacuum or partial vacuum) in the water supply system. This can occur when there’s a water main break, high water demand from firefighting, or when pumps create suction. Back siphonage can draw contaminants into the potable water system through submerged inlets or cross-connections.

Backflow

Backflow is the unwanted reversal of water flow in a piping system, allowing non-potable water or other substances to enter the potable (drinking) water supply. This can occur through either back-siphonage or back pressure and poses serious health risks to water consumers.

Backflow Preventer

A backflow preventer is a mechanical device or assembly installed in a plumbing system to prevent the reverse flow of water. These devices use check valves, air gaps, or reduced pressure zones to ensure water flows in only one direction, protecting the potable water supply from contamination.

Check Valve

A check valve is a mechanical device that allows fluid to flow in only one direction. It automatically closes when flow attempts to reverse. While check valves are components of many backflow preventers, a single check valve alone is not considered adequate backflow protection for high-hazard applications.

Containment

Containment refers to backflow protection at the water service connection, preventing contamination from entering the public water distribution system. This is typically achieved by installing an approved backflow preventer at or near the property line or water meter, protecting the municipal water supply from potential hazards within a facility.

Contaminant

A contaminant is any physical, chemical, biological, or radiological substance or matter in water that can cause illness, death, or pose a health hazard. In backflow prevention, contaminants include chemicals, bacteria, waste products, and any other substances that could compromise water quality and safety.

Cross-Connection

A cross-connection is any actual or potential connection between a potable water system and any source of contamination or non-potable water. This includes permanent piping arrangements as well as temporary connections such as hoses. Cross-connections are the pathways through which backflow can occur.

Cross-Connection Control

Cross-connection control is a program or set of practices designed to identify, eliminate, or protect against cross-connections in water systems. This includes surveys, device installation, testing, maintenance, and education to prevent backflow incidents and protect public health.

Cross-Connection Survey

A cross-connection survey is a systematic inspection of a facility’s water system to identify actual and potential cross-connections. Conducted by certified specialists, these surveys assess hazard levels and recommend appropriate backflow prevention devices to ensure compliance with regulations.

Double Check Valve Assembly (DCVA)

A double check valve assembly consists of two independently operating check valves with test cocks and shut-off valves. It provides protection against both back-siphonage and back pressure in low to moderate hazard applications. DCVAs must be tested annually to ensure proper operation.

Dual Check Valve

A dual check valve is a compact device containing two check valves in series without test cocks. While it provides basic backflow protection for residential services, it cannot be tested in place and is typically used as containment protection at residential water meters.

Hazard Assessment

Hazard assessment is the process of evaluating the degree of potential health risk posed by a cross-connection. Hazards are typically classified as high (contamination), moderate (pollution), or low risk, determining the type of backflow prevention required.

High Hazard

A high hazard cross-connection poses a risk of contamination that could cause illness or death. Examples include connections to sewage systems, chemical processes, medical facilities, and industrial operations. High hazard situations require maximum protection, typically a reduced pressure principle assembly or air gap.

ICI Properties

ICI properties refer to Industrial, Commercial, and Institutional facilities. These properties typically have complex water systems with multiple potential cross-connections and are subject to mandatory backflow prevention programs and regular testing requirements.

Isolation

Isolation (also called premise isolation) refers to backflow protection installed within a facility to protect specific equipment or areas from contamination. This internal protection complements containment devices and prevents cross-contamination between different water uses within a building.

Low Hazard

A low hazard cross-connection poses minimal health risk but could affect the aesthetic quality of water (taste, odor, or color). Examples include connections to heating systems without chemicals or food service equipment. Low hazard applications typically require double check valve assemblies.

Moderate Hazard

A moderate hazard cross-connection presents a pollution risk that could cause minor illness or aesthetic concerns. Examples include connections to cooling systems with approved chemicals, some commercial equipment, and certain irrigation systems. Protection typically requires a double check valve assembly or reduced pressure principle assembly.

Non-Potable Water

Non-potable water is water that is not safe for human consumption. This includes recycled water, irrigation water, cooling water, and any water that has been used in industrial processes. Non-potable water systems must be completely separated from potable water systems or protected by appropriate backflow prevention.

OWWA

The Ontario Water Works Association (OWWA) is the authoritative body for water professionals in Ontario. OWWA develops training programs, certifies Cross-Connection Control Specialists, and establishes standards for backflow prevention programs throughout the province.

Potable Water

Potable water is water that meets drinking water standards and is safe for human consumption. Protecting potable water from contamination through cross-connections is the primary goal of backflow prevention programs.

Pressure Vacuum Breaker (PVB)

A pressure vacuum breaker is a backflow prevention device consisting of a check valve and an air inlet valve. It protects against back-siphonage only and can be used under continuous pressure. PVBs must be installed at least 300mm (12 inches) above the highest point of water use and are commonly used in irrigation systems.

Reduced Pressure Principle Assembly (RP/RPZ)

A reduced pressure principle assembly is the most protective mechanical backflow preventer, consisting of two check valves with a pressure-monitored chamber between them. The relief valve opens if either check valve fails, providing protection against both back-siphonage and back pressure in high-hazard applications.

Relief Valve

A relief valve is a component of reduced pressure principle assemblies that opens to atmosphere when the pressure in the zone between check valves approaches supply pressure. This discharge indicates a malfunction and prevents contaminated water from entering the potable supply.

Test Cock

Test cocks are small valves on testable backflow preventers that allow certified testers to connect gauge equipment and verify proper operation. Most testable assemblies have multiple test cocks to measure pressures at different points within the device.

Thermal Expansion

Thermal expansion occurs when water is heated and expands in a closed system, potentially creating back pressure. Backflow preventers can create closed systems, requiring thermal expansion tanks or relief valves to manage pressure increases from water heaters.

Water Purveyor

A water purveyor is the entity responsible for supplying potable water to consumers. This includes municipalities, regional water authorities, and private water companies. Water purveyors are mandated to implement cross-connection control programs to protect public water supplies.

Zone Protection

Zone protection involves installing backflow preventers at specific hazard points within a facility, rather than just at the main service connection. This approach provides multiple layers of protection and prevents cross-contamination between different areas or processes within a building.

This glossary is maintained by Spec-Mark Group to help property owners, facility managers, and water professionals understand important backflow prevention terminology. For specific requirements in your area, consult your local water authority or a certified Cross-Connection Control Specialist.