Water Delivery Systems

Why are Backflow Preventers important?

Protecting the Water Supply


Clean water is a resource we in America have come to take for granted: We enjoy drinking, cooking, bathing, and using it for many other activities on demand flowing right out of our taps. But do we understand that this always-available water may pose a serious public health threat if not properly managed?

This resource we depend upon is trustworthy because it is treated by the water supplier according to Federal and State quality standards. Once the water is made potable (drinkable), the supplier wants to protect it from contamination and pollution while delivering it to the consumer (end user).

But water suppliers have no control over what happens to water in the end user's plumbing. The end user may be a home, apartment building, a farm, an office high-rise, a park, a heavy industrial building or any number of other facilities. The point of connection between the water supplier's system and the end user's plumbing--usually the water meter--exposes all other people on the system to the activities of each end user.

How can the water meter pose a threat to public health?

Water systems use positive pressure to deliver water from the treatment facility to the consumer. We might assume that the water always flows in one direction. However, pressure differences and changes in the system may result in water flowing in the reverse of its normal direction. This is not a problem unless part of the system is cross-connected to a substance other than potable water. If water in the end user's system is mixed with pollutants or contaminants, a pressure gradient can move that mixture into the user's plumbing, through the water meter, and into the community water supply.

This is the definition of the term "backflow". Backflow can cause substances other than water to enter the safe drinking water supply. These unwanted substances may then be delivered to other users of the water system (read: you and me). So in order to protect against contamination or pollution threatening the public health, backflow prevention assemblies are required to be installed and properly maintained.

Backflow can occur because of a drop in the delivery pressure of the supply system. This pressure drop "pulls" water from the end user. For example, backsiphonage might occur when an underground water line breaks, or during the fighting of a fire. Water is "pulled" from surrounding users to the location of greatest use or the point of escape.

Backflow can also happen when the water pressure on the end user's side exceeds the pressure in the supply system. This high pressure "pushes" the water and anything in the end user's system back into the public delivery system. This potential exists when the end-user's plumbing is equipped with items such as pumps, boilers, chillers, dip tanks, etc. The carbonation tank at convenience store soda machines, and even the height of tall buildings can cause backpressure.

When either back-siphonage or backpressure occurs, pollutants and/or contaminants can backflow into the distribution system and will be delivered to nearby users when the next tap is opened.

What does a Backflow Preventer do and why must it be tested

Water suppliers must protect the quality of water up to the point of delivery to the end user. Backflow prevention assemblies are used to provide a separation between the delivery system and end user. Water users may also install backflow assemblies internally to protect themselves, their families, customers and employees from known hazards within their own properties.

Backflow assemblies are mechanical devices with specific design requirements. Most backflow assemblies are evaluated by the Foundation for Cross-Connection Control and Hydraulic Research at the University of Southern California. The Foundation's approval process involves stringent laboratory and field tests. Assemblies which successfully pass these tests are granted Approval. In all water districts of San Diego County backflow preventers must recieve USC approval in order to be used for protection of the water supply.

As with all things mechanical, break-downs are inevitable. Since backflow prevention assemblies are health safety devices, it is important to catch a break-down before it leads to an incident. Backflow assemblies must be field tested immediately after installation and at least once each year to ensure they are working properly. When a field test determines that a device is not working properly, the assembly must be repaired and retested. Field testing must be performed by a certified backflow prevention assembly tester, using an approved and properly calibrated test gauge.

A certified backflow tester is someone who has successfully completed a course of instruction in backflow prevention assemblies which includes theory, design, performance, testing, and maintenance. Upon successful course completion which includes both written and performance examinations, the backflow tester certification is issued. The certification for a backflow tester in San Diego lasts for 3 years and is issued by AWWA or ABPA. Some jurisdictions in the County also accept ASSE certification. Prior to certificate expiration, the tester must again successfully complete both written and performance examinations in order to keep their certification active.

Providing a clean and safe water delivery system free from objectionable impurities requires the cooperation of water providers, end users and certified backflow prevention assembly testers. Please join with us in helping to protect our drinking water system and keeping safe water flowing to our taps.