Show/Hide

Frequently Asked Questions

Print
  • What is a cross-connection?
  • What is backflow?
  • What is back-pressure  backflow?
  • What is back-siphonage?
  • Why does the Brownsville Public Utilities Board need to control cross-connections and protect its public water system against backflow?
  • What should a water supplier do to control cross-connections and protect its public water system against backflow?
  • What is a backflow preventer?
  • What is an air gap?
  • What is a reduced principle backflow assembly (RPBA)?
  • What is a pressure vacuum breaker assembly (PVB)?
  • What is a double check valve assembly (DCVA)?
  • Why do backflow preventers have to be tested periodically?

Q. What is a cross-connection?

A. A cross-connection is any temporary or permanent connection between a public water system or consumer's potable (i.e., drinking) water system and any 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.

Q. What is backflow?

A. Backflow is the undesirable reversal of flow of non-potable water or other substances through a cross-connection and into the piping of a public water system or consumer's potable water system. There are two types of backflow - back-pressure  backflow and back-siphonage.

Q. What is back-pressure  backflow?

A. Back-pressure 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. Back-pressure  (i.e., downstream pressure that is greater than the potable water supply pressure) can result from an increase in downstream pressure, a reduction in the potable water supply pressure, or a combination of both. Pumps can create increases in downstream pressure; temperature increases in boilers, etc. Reductions in potable water supply pressure occur whenever the amount of water being used exceeds the amount of water being supplied, such as during water line flushing, firefighting or breaks in water mains.

Q. What is back-siphonage?

A. Back-siphonage is backflow caused by a negative pressure (i.e., 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 nearby firefighting, a break in a water main, etc.

 

Q. Why does the BPUB need to control cross-connections and protect its public water system against backflow?

A. Backflow into a public water system can pollute or contaminate the water in that system (i.e., backflow into a public water system can make the water in that system unusable or unsafe to drink), and each water supplier has a responsibility to provide water that is usable and safe to drink under all foreseeable circumstances. Furthermore, consumers generally have absolute faith that water delivered to them through a public water system is always safe to drink. For these reasons, BPUB must take precautions to protect its public water system against backflow.

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

A. The Texas Commission on Environmental Quality gives public water suppliers two options: 1. Require a backflow prevention assembly at each service connection that may create a threat to the public water supply. 2. Require backflow prevention assemblies and assemblies within a premises as outlined in 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 prevention assembly required under the State Plumbing Code is not properly installed or maintained; (4) classified or restricted facilities; and (5) tall buildings.

Q. What is a backflow preventer?

A. A backflow preventer is a means or mechanism to prevent backflow. The basic means of preventing backflow is an air gap, which either eliminates a cross-connection or provides a barrier to backflow. The basic mechanism for preventing backflow is a mechanical backflow preventer, which provides a physical barrier to backflow. The principal types of mechanical backflow preventers are the reduced-pressure principle assembly, the pressure vacuum breaker assembly, and the double check valve assembly.

Q. What is an air gap?

A. 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. This separation must be at least twice the diameter of the water supply outlet and never less than one inch. An air gap is considered the maximum protection available against back-pressure  backflow or back-siphonage but is not always practical and can easily be bypassed.

Q. What is a reduced principle backflow assembly (RPBA)?

A. An RPBA is a mechanical backflow prevention assembly that consists of two independently acting, spring-loaded check valves with a hydraulically operating, mechanically independent, spring-loaded pressure differential relief valve between the check valves and below the first check valve. It includes shutoff valves at each end of the assembly and is equipped with test cocks. An RPBA is effective against back-pressure  backflow and back-siphonage and may be used to isolate health or non-health hazards.

Q. What is a pressure vacuum breaker assembly (PVB)?

A. Two styles of PVBs are available: (1) Pressure Vacuum Breaker and (2) Spill Resistant Vacuum Breaker. A PVB is a mechanical backflow prevention assembly that consists of an independently acting, spring-loaded check valve and an independently acting, spring-loaded air inlet valve on the discharge side of the check valve. It includes shutoff valves at each end of the assembly and is equipped with test cocks. A PVB may be used to isolate health or non-health hazards but is effective against back-siphonage only.

 

Q. What is a double check valve assembly (DCVA)?

A. A DCVA is a mechanical backflow prevention assembly that consists of two independently acting, spring-loaded check valves. It includes shutoff valves at each end of the assembly and is equipped with test cocks. A DCVA is effective against back-pressure  backflow and back-siphonage but should be used to isolate only non-health hazards.

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

A. To ensure the proper operation of a backflow prevention assembly, it must be tested and certified upon installation and at least once a year thereafter if installed to protect from a health hazard situation. The Texas Commission on Environmental Quality and local water suppliers oversee these state requirements. Mechanical backflow prevention assemblies have internal seals, springs and moving parts that are subject to fouling, wear or fatigue. Also, mechanical backflow preventers and air gaps can be bypassed. Therefore, all backflow prevention assemblies have to be tested periodically to ensure that they are functioning properly. Mechanical backflow prevention assemblies have to be tested with properly calibrated gauge equipment.