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Environmental Health Division
The Minnesota Department of Health has been stepping up efforts to educate water operators, property owners, and citizens about problems associated with backflow.
Backflow, or backsiphonage, occurs when the pressure of a polluted source exceeds that of the potable water. It can result in contaminants, including hazardous chemicals and bacteria, mixing with potable water.
Cross connections—an actual or potential connection between a potable and non-potable water supply—are sources of backflow problems. The Minnesota Department of Health has been identifying hazardous cross connections within public water supply distribution systems and designating them as significant deficiencies. Hazardous cross connections are defined as situations in which potential contaminants could cause waterborne disease or illness and in which there is a possibility of the contaminants entering the drinking water supply. Public water suppliers with hazardous cross connections will be required to remove or correct them.
Backflow and cross connections are a concern among commercial and residential property owners, as well. A garden hose can often be a cross connection. Someone spraying a commercial weed killer using a cross connection could have some of the weed killer sucked back into the hose, especially if there is a drop in the water pressure while the herbicide is attached. In this case, the person could be poisoned by taking a drink from the hose after disconnecting the weed killer.
In commercial buildings, backsiphonage of chemicals could cause contaminants to enter the building’s distribution-system water mains. Backflow of boiler corrosion control chemicals into an office building’s water supply is also possible. In addition to public water systems, property owners are advised to develop a cross-connection control and backflow prevention program. These programs can prevent the costs of responding to contamination situations.
In residential or commercial buildings hose and/or spray device use, atmospheric vacuum breakers (AVB) can provide excellent, inexpensive protection against backsiphonage (but not backpressure). The potable water supply is protected as long as sufficient water pressure maintained (and no pressurization is added to the end of the hose or other attachment). AVBs are generally available in ½- to 3-inch sizes. Consumers should note that AVBs must be installed vertically, at least 6 inches higher than the final outlet (or flood-level rim of a vessel), and must not have any shutoffs downstream.
Hose bibb vacuum breakers are a common, specialized variety of AVB normally attached to sill cocks in order to protect potable water flowing through garden hoses, slop sink hoses, or spray outlets. If freezing is a concern, the consumer should look for drainable models. Some models also are designed to be tamper-proof.
The Minnesota Department of Health and American Water Works Association recommend the following precautions:
- Do not submerge hoses in buckets, pools, tubs, or sinks.
- Keep the end of the hose clear of possible contaminants.
- Do not use spray attachments without a backflow prevention device, and attach these devices to all threaded faucets around the home. Such devices are inexpensive and available at hardware stores.
- If a plumber is used to install backflow prevention devices, make sure the plumber is licensed to ensure that local codes and manufacturer’s recommendations are met.
- Commercial property owners should develop a plan for flushing or cleaning the water system to minimize the risk of drawing contaminants into uncontaminated areas.
- Maintain air gaps (vertical separations between an outlet and the flood-level rim of a vessel of at least twice the diameter of the water supply outlet and at least one inch) between hose outlets and any liquids.