The seven deadly sins of cross connection
By Danny Wilson
Polluted or contaminated fluids (and) sometimes other materials) can enter drinking water piping through backflow and or back-siphonage in the water system. In other words, the water is flowing in the reverse direction to which it was intended. In most cases this reverse flow cannot be seen when it occurs.
These cross connections, whether actual or potential, can be eliminated through the use of an air gap. When an air gap is not possible or appropriate, cross connection risk can be reduced by using approved backflow prevention devices and assemblies.
Depending on the hazard of the connection (minor, moderate or severe) an appropriate approved backflow preventer device or assembly would be installed to protect the potable water system.
Sin No. 1: The Hose Bibb
The ever-popular hose bibb, found in homes and buildings throughout Canada, is thought to be
the most common offender that can lead to a cross connection. A connected hose with an open end can be immersed into mixing pails, tubs or sinks, or may be laying on the ground in a pool of water, which can create a potential or actual cross connection allowing fluids other than drinking water back into the building water supply.
If a building loses water pressure, perhaps from a water main break or if the building’s water is turned off by a repairman, the contaminated contents of the pail or pool of water on the ground can be back-siphoned into the drinking water lines of the building. When the water pressure is restored, the contaminated water is now distributed through the drinking water system.
Corrective action: Properly install a hose connection vacuum breaker to control the cross connection, or use a wall hydrant (frost-free hose bibb) with a built-in vacuum breaker.
Sin No. 2: The Service Sink Faucet
Normally found in schools and commercial buildings, the service sink faucet can create a cross connection through the faucet when a hose is attached. If the flexible service sink hose is immersed and filling a pail with cleaning chemicals, the potential exists for backflow if the water pressure is lost in the building.
Corrective action: Install an approved hose connection vacuum breaker on the service sink faucet or switch out the faucet for a modern one with a built-in atmospheric vacuum breaker.
Sin No. 3: The Y Fitting
This use of Y fittings, a rubber hose that gets connected to the hose thread of a service sink faucet to provide two outlet valves, is very concerning, and unfortunately happens too often. Once the service sink’s hot and cold handles are opened, the cleaner has two outlets rather than one to use at the sink. A problem can occur, however, when the cleaner does not close the hot and cold faucet handles, only stopping flow at each end of the Y.
This puts constant pressure on the atmospheric vacuum breaker that is typically found in the faucet spout. These atmospheric vacuum breakers are designed for a maximum of 12 hours of continuous use, after which they can get frozen in a closed position, becoming inoperative. A failed atmospheric vacuum breaker provides only a false sense of protection.
Corrective action: Remove the rubber Y fitting immediately and inform the person responsible about this potentially dangerous connection.
Sin No. 4: Chemical Dispensers
Wherever cleaning chemicals are added to a water system, a severe hazard is created. An approved backflow preventer must be used to protect from these chemicals backflowing and entering the drinking water system.
Corrective action: The installation of an approved Reduced Pressure Principle Assembly (RP) backflow preventer to isolate the water lines serving the chemical line connections. Alternatively, the installation of an approved air space vacuum breaker.
Sin No. 5: Boilers
Most heating systems have a connection to a potable water line to maintain the boiler water pressure. An approved backflow preventer must be used to protect the potable water where a direct water connection is used. If chemicals are used in the heating system’s fluids, to protect the boiler from corrosion or freeze ups, a backflow preventer that is approved for this severe hazard application must be used.
Corrective action: Install an approved RP backflow preventer for a direct water line connection, or eliminate the direct water line connection by using a separate, self-contained pressurized boiler water supply.
Sin No. 6: Toilets and Urinals
Water closets typically have direct connections to the potable water supply, and must therefore use an approved backflow prevention device on the plumbing fixture to protect the water system from potential siphonage of fecal material and urine back into the potable water lines.
Corrective action: A residential tank style WC will use a ballcock with an approved anti-siphon device. A commercial flushometer style toilet or urinal will use an approved atmospheric vacuum breaker to suit the flushometer valve.
Sin No. 7: Sinks, Baisins and Tubs
Kitchen sinks, wash basins and bath tubs all have hot and cold potable water connections and are designed to use an air gap, considered to be the most effective method of preventing a cross connection.
The air gap is the actual open-air space below the outlet of the faucet spout and the flood level rim of the plumbing fixture it serves. This feature physically prevents any pollutants or contaminates from entering the faucet spout and water lines by back-siphonage. However, the addition of a hose to the spout of the plumbing fixture can circumvent the air gap.
Corrective action: Ensure the air gap height is a minimum of 2 times the effective opening (measured as a pipe diameter) of the faucet spout and never less than 1” in height. If a hose is connected to a plumbing fixture spout and there is no approved atmospheric vacuum breaker installed, the hose must be removed to re-establish the air gap protection.