A cross connection is any temporary or permanent connection between a public water system or consumer's potable (i.e., drinking) water system and any source or system containing non-potable water or other substances. An example is the piping between a public water system or consumer's potable water system and an auxiliary water system, cooling system, or irrigation system.

Cross connections can occur at many points throughout a distribution system and a community's plumbing infrastructure. Cross connections can be identified by looking for physical interconnections (or arrangements) between a customer's plumbing and the water system. Some specific examples of backflow incidents that can occur are:

• Lawn chemicals backflowing (backsiphoning) through a garden hose into indoor plumbing and potentially into the distribution system.
• Backsiphonage of "blue water" from a toilet into a building's water supply.
• Carbonated water from a restaurant's soda dispenser entering a water system due to backpressure.
• Backsiphonage of chemicals from industrial buildings into distribution system mains.
• Backflow of boiler corrosion control chemicals into an office building's water supply.

Backflow into a public water system can pollute or contaminate the water in that system. For instance, backflow into a public water system can make the water in that system unusable or unsafe to drink. Each water supplier has a responsibility to provide water that is usable and safe to drink under all foreseeable circumstances. Furthermore, consumers generally have absolute faith that water delivered to them through a public water system is always safe to drink. For these reasons, each water supplier must take reasonable precautions to protect its public water system against backflow.

A DC is a mechanical backflow preventer that consists of two independently acting, spring-loaded check valves. It includes shutoff valves at each end of the assembly and is equipped with test cocks. A DC is effective against backpressure backflow and backsiphonage but should be used to isolate only non-health hazards.

A PVB is a mechanical backflow preventer that consists of an independently acting, spring-loaded check valve and an independently acting, spring-loaded, air inlet valve on the discharge side of the check valve. It includes shutoff valves at each end of the assembly and is equipped with test cocks. A PVB may be used to isolate health or non-health hazards but is only effective against backsiphonage.

An RP is a mechanical backflow preventer that consists of two independently acting, spring-loaded check valves with a hydraulically operating, mechanically independent, spring-loaded pressure differential relief valve between the check valves and below the first check valve. It includes shutoff valves at each end of the assembly and is equipped with test cocks. An RP is effective against backpressure backflow and backsiphonage and may be used to isolate health or non-health hazards.

An air gap is a vertical, physical separation between the end of a water supply outlet and the flood-level rim of a receiving vessel. This separation must be at least twice the diameter of the water supply outlet and never less than one inch. An air gap is considered the maximum protection available against backpressure backflow or backsiphonage but is not always practical and can easily be bypassed.

Mechanical backflow preventers have internal seals, springs, and moving parts that are subject to fouling, wear, or fatigue. Also, mechanical backflow preventers and air gaps can be bypassed. Therefore, all backflow preventers must be tested periodically to ensure that they are functioning properly. A visual check of air gaps is sufficient, but mechanical backflow preventers need to be tested with properly calibrated gauge equipment.

The responsibilities of an owner of a cross connection are defined in the Massachusetts Department of Environmental Protection’s Cross Connection Control Program Regulations - 310 CMR 22.22 (refer to mass.gov/doc/310-cmr-2222-cross-connection-regulations-0/download). Per 310 CMR 22.22 (4), the owner of any cross connection protected by a double check valve assembly or reduced pressure backflow preventer shall:

• (a) Notify the public water system of all cross connections protected by a double check valve assembly or reduced pressure backflow preventer and comply with all necessary approvals and permits from the public water system and/or the Department [MassDEP] for the maintenance of cross connections, as specified at 310 CMR 22.22;
• (b) Have suitable arrangements made so that inspections of backflow prevention devices and cross connection surveys can be made during regular business hours;
• (c) Maintain a spare parts kit and any special tools required for the removal and reassembly of backflow prevention devices;
• (d) Provide the necessary labor for inspection and testing by the Certified Backflow Prevention Device Testers or Certified Cross Connection Surveyor;
• (e) Overhaul, repair, or replace within 14 days of the initial inspection date and retest pursuant to 310 CMR 22.22(13)(e), any device which fails a test or is found defective;
• (f) Submit copies of the Inspection and Maintenance Report Form as required by the public water system.
• (g) Maintain on the premises complete records on all devices for the life of said devices including as-built plans and design data sheets; maintain for seven years the Inspection and Maintenance Report Forms for tests conducted by the certified.
• (h) Make certain that the cross connection protection device is tested as specified at 310 CMR 22.22(13) or as required by the public water system.

For Aquarion’s rules and regulations, including regarding Cross Connections, visit our Rules and Regulations page.