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1. What is a cross-connection?

A cross-connection is any temporary or permanent connection between a public water system or consumer's potable (e.g., drinking) water system and a 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. For more information please call 512-393-8010.

2. What is backflow?

Backflow is the reversal of flow of water or other substances through a cross-connection into the public water system or consumer's potable water system. There are 2 types of backflow... Backpressure backflow and back-siphonage. For more information please call 512-393-8010.

3. What is backpressure backflow?

Backpressure backflow is backflow caused by a downstream pressure that is greater than the upstream or supply pressure in a public water system or consumer's potable water system. Backpressure can result from an increase in downstream pressure, a reduction in the potable water supply pressure, or a combination of both.

Causes of increases in downstream pressure:
- Pumps (such as wells and booster pumps)
- Temperature increases in boilers, etc.

Causes of decreases in downstream pressure:
- Breaks in water mains
- Fire fighting
- Water line flushing

For more information please call 512-393-8010.

4. What is back-siphonage?

Back-siphonage is backflow caused by a negative pressure (e.g., a vacuum or partial vacuum) in a Public water system or consumer's potable water system. The effect is similar to drinking water through a straw. Back-siphonage can occur when there is a stoppage of water supply due to a nearby fire fighting, a break in a water main, etc. For more information please call 512-393-8010.

5. Why does the Water / Wastewater Utilities Department need to control cross-connections and protect its public water system against backflow?

Backflow into a public water system can pollute or contaminate the water in that system making it 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 have faith that water delivered to them through a public water system is safe to drink. Therefore, the Water/Wastewater Utilities Department must take precautions to protect its public water system against backflow. For more information please call 512-393-8010.

6. What should a water supplier do to control cross-connections and protect their public water systems against backflow?

The Texas Commission on Environmental Quality gives public water suppliers 2 options:
- Require backflow prevention at each service connection that may create a threat to the public water supply.
- Require backflow devices and assemblies within a premise as outlined the state required plumbing codes.

The water suppliers usually do not have the capability to repeatedly inspect every consumer's premises for cross-connections and backflow protection. Generally, this would include the water service connection to each dedicated fire protection system or irrigation piping system and the water service connection to each of the following types of premises:
(1) Premises with an auxiliary or reclaimed water system
(2) Industrial, medical, laboratory, marine or other facilities where objectionable substances are handled in a way that could cause pollution or contamination of the public water system
(3) Premises exempt from the State Plumbing Code inspection and premises where an internal backflow preventer required under the State Plumbing Code is not properly installed or maintained
(4) Classified or restricted facilities
(5) Tall buildings

For more information please call 512-393-8010.

7. What is a backflow preventer?

A backflow preventer is a means or device which prevents pollutants and contaminants from flowing into the public water system. For more information please call 512-393-8010.

8. What is an air gap?

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. Find more information regarding air gaps.

9. What is a reduced pressure zone assembly?

A reduced pressure zone assembly protects water from substances that may contaminate water causing illness or death. Find more information regarding pressure zones.

10. What is a double-check valve assembly?

A double-check valve assembly protects water from substances that may pollute but not contaminate the water. Find more information about double-check valves.

11. What is a hose bibb vacuum breaker?

A hose bibb vacuum breaker (HBVB) is one of the least expensive and most commonly used backflow preventers. Find more information regarding bibb vacuum breakers.

12. Where can I get more information about cross-connection control?

Find more information about cross-connection control

13. Why do backflow preventers have to be tested periodically ?

In order to insure the proper operation of a backflow assembly, it must be tested and certified upon installation and periodically thereafter as required by state code. If the hazard (substance you are protecting against) is considered a high hazard (e.g., a hazard that can cause health problems), the City requires that the device be tested annually.

If the hazard is considered a low hazard (e.g., the hazard effects only the taste and odor of the water), the City requires testing every 3 years. The Texas Commission on Environmental Quality oversees the state requirements. For more information please call 512-393-8010.

14. Why does a soft drink dispensing machine require backflow protection?

Soft drink dispensers (post-mix carbonators) use carbonated water mixed under pressure with syrup and water to provide soft drinks beverages. Many, if not most water pipes are made of copper. When carbonated water comes into contact with copper, it chemically dissolves the copper from the pipe. This copper-carbonate solution has been proven to be a risk to the digestive system. For more information please call 512-393-8010.