What is it? 

Backflow is the unwanted reversal of the flow of water and substances. Typically, water will flow from the public water supply to the consumer’s plumbing system. When backflow occurs, the water flows from the non-drinking water source to the drinking water source and potentially contaminates it.

What causes it?

Backflow incidents are caused by one of the following:

• Back pressure — This is created when the pressure within the customer’s system becomes greater than the water supply pressure. Elevated tanks, heating systems and booster pumps are some of the main causes of back pressure.

• Back siphonage — This is created when the water supply main has negative or reduced pressure. Water main breaks or hydrant flushing are two of the main causes of back siphonage.

The town has requirements to protect the public drinking water supply.

• Containment Protection — The town installs backflow prevention at the service meter to protect the public water supply from contamination. 

• Isolation Protection — The town requires backflow prevention at the fixture where water is used. This protects the customer's internal drinking water plumbing from contamination.

Several types of facilities are required to install a backflow prevention device. If your property or business type is not included in the list below and you have a specific question about your legal requirements, contact the town's utilities infrastructure protection supervisor.

• Auto repair shops
• Auxiliary water supply (wells)
• Barber shops and beauty salons
• Breweries
• Buildings that reuse or recycle water
• Buildings with commercial or public kitchens, groundwater wells, multiple water service lines, roof tanks and elevated storage lines, or water-cooled equipment or chillers
• Canneries
• Commercial car washes
• Dye plants
• Exterminators
• Fire sprinkler system
• Food preparation facilities
• Food processing plants and meat or fish packers
• Funeral parlors
• Greenhouses
• Lawn irrigation systems
• Metal plating, cleaning, processing or fabricating facilities
• Hospitals, clinics and laboratories (including veterinary hospitals)
• Ice manufacturing facilities
• Large residential dwellings with water boilers that use rust-inhibitors or other water treatment chemicals (treated water boilers)
• Laundries and dry cleaners
• Medical and dental offices
• Morgues, mortuaries and autopsy facilities
• Nursing homes
• Paper processors
• Photo-processing facilities
• Printing facilities
• Schools and colleges
• Sewage treatment plants or handling facilities
• Slaughterhouses and live poultry processing facilities
• Swimming pools
• Supermarkets
• Tanneries
• Warehouses with toxic chemical storage

The town prohibits direct connections between the water supply and any potential source of contamination. Potential sources of contamination must be isolated by an air gap or a reduced pressure zone backflow assembly. 

A direct connection would occur if a garden hose became submerged in a swimming pool, hot tub, soapy water bucket, pond or pet water dish.

Water Use by Businesses

Contracted businesses working in Hillsborough and needing water must do one of the following:

• Transport water into town.
• Purchase bulk water from the town.
• Rent a hydrant meter from the town. The orange box that is connected to some hydrants contains a meter and a backflow prevention device. 

• Start or Stop Service page for bulk water purchases or hydrant meter rentals
• Tampering and Theft page

The town requires a hose bib vacuum breaker on every outside faucet. The vacuum breaker must be certified by the NSF 61 standard.

The American Water Works Association recommends replacing vacuum breakers every five years or if they are failing. The device has failed if water is spraying out of the breaker's weep holes. 

The town contracts with Backflow Solutions to manage its backflow test data. Customers using backflow prevention assemblies must:

• Have the assemblies tested when installed.
• Maintain their assemblies and have them tested annually by qualified individuals.
• Submit results of testing and maintenance to Backflow Solutions.

The company maintains a list of licensed, registered testing agencies on its website.

Contact Backflow Solutions at 800-414-4990 or bsionline@backflow.com. Visit its website at BSI Online.

Process

• Existing Assemblies — Licensed testers must submit test results through the Backflow Solutions website.

• Failed Test — The assembly must be repaired within 10 days if it fails a test. A certified tester must submit retest results on the Backflow Solutions website.

• New Installations — A licensed tester who performed the work must sign a printed test form. A copy must be emailed to Backflow Solutions.

Air Gap — An air gap is the vertical space between a water inlet and the rim of a receptacle receiving public water. Examples are a faucet or hose providing water to a bucket, sink or pool. The air gap must be at least twice the diameter of the water inlet and no smaller than 1 inch.

Backflow Assembly — This mechanical unit prevents backflow. It does not have inlet and outlet shutoff valves. It has four test cocks, making inline testing possible. Public water systems, which regulate connections to the public water supply, generally require backflow assemblies rather than devices.

Backflow Device — This mechanical unit prevents backflow. It does not have inlet or outlet shutoff valves and usually does not have test cocks. Inline testing is not possible for devices without test cocks. The devices are not approved by the University of Southern California Foundation for Cross-Connection Control and Hydraulic Research. Backflow devices generally are governed by plumbing code when a building is constructed or upfitted. 

Elimination — Eliminating the cross-connection is necessary when the hazard has been improperly installed and plumbed or when the hazard is no longer in use.

Double Check Valve Assembly 

• Non-health hazards
• Back pressure/back siphonage
• Fire sprinkler system with no booster pumps, most commercial establishments

Double Check Valve Detector Assembly 

• Non-health hazards
• Back pressure/back siphonage
• Fire sprinkler systems that are classified as non-health hazards

Reduced Pressure Detector Assembly 

• Health and non-health hazards
• Back pressure/back siphonage
• Fire sprinkler systems that are classified as health hazards

Reduced Pressure Principal Assembly (preferred assembly) 

• Health and non-health hazards
• Hospitals, car washes, lawn irrigation, mortuaries

Pressure Vacuum Breaker

• Back siphonage only
• Multi-zone irrigation systems

Hose Connection Vacuum Breaker (not testable)

• Back siphonage only
• Garden hose connections

All backflow devices are required to be in a class 1 or 2 enclosure that meets the American Society of Sanitary Engineering’s 1060 standard. These enclosures help protect against frost and freezing. 

• Backflow devices can be protected in winter with pipe insulation, an insulated cover or a heat lamp and heat trace tape.

• Backflow devices for irrigation can be removed for winterization. They must be retested when reinstalled in the spring. 

Due to the risk for backflow, the town recommends that customers filling swimming pools, hot tubs, ponds or other bodies of water:

• Use the air gap method. See the section on backflow prevention methods.
• Avoid times when hydrants are opened for flushing. This occurs in March and occasionally in the fall.

Water System Flushing

Lower Water Pressure — When hydrants are flushed, pressure in the water system drops. Water could backflow into the public water supply system if water main pressure is lower and a hose becomes submerged in a body of water being filled.

Chemical Change — During the annual March flushing, the town’s water is disinfected by chlorination instead of chloramines (ammonia and chlorine). The state requires this change in disinfection for one month each year. The change could upset the balance of a pool, pond or spa.