Backflow refers to the reverse flow of nonpotable water, or other substances, through a cross-connection and into the piping of a public water system or customer’s potable water system. Two types of backflow are backpressure backflow and back-siphonage.

Backpressure backflow occurs when the downstream side of the piping system is greater than the supply pressure in a public system or customer’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. 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 waterline flushing, fire fighting or breaks in water mains.

Back-siphonage is backflow caused by negative pressure (i.e. vacuum or partial vacuum) in a public water system or customer’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 fire fighting, a break in a water main, etc.

A cross-connection is any temporary or permanent connection between a public water system or the customer’s potable water system and any source or system containing nonpotable water or other substances.Common cross-connections:

  • Private wells – where the private well connection is connected to a service line receiving water from a public water supply. The untreated water could be pumped into the potable water supply which serves the home and the public water system.
  • Lawn sprinkler systems – where the stagnant/contaminated water from the sprinkler system could be drawn into the drinkable water supply for your home.

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

The program safeguards the public drinking water and protects the health of its customers by ensuring that any contaminants that could backflow into the public water supply system are isolated within the customer’s internal distribution system.

Proper permits must be acquired for installation of the backflow prevention assembly. Additional information can be obtained from the authority having jurisdiction in your service area.

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 correctly. Mechanical backflow prevention assemblies have to be tested with properly calibrated gauge equipment.

In order to insure the proper operation of a backflow prevention assembly, it must be tested and certified upon installation and at least once a year thereafter by a licensed backflow tester.

A list of accredited companies can be found at SAWS Cross-Connection and Backflow Prevention Program. The list will also be provided with your annual test notice.

It is to our understanding that fees ranges in price from $40 and up, so please call around when you are trying to schedule with a tester.

The licensed tester will complete a “Test & Maintenance Report” (T & M) documenting the results. The completed T & M form must be returned to SAWS Backflow Prevention Section.

Contact SAWS Backflow Prevention Inspection Section at or 210-233-2910.

Yes. Section 608.16.5, of the Plumbing and Fuel Gas Code, connections to lawn irrigation systems, states that the potable water supply to lawn irrigation systems shall be protected against backflow by a pressure-type vacuum breaker, a double-check valve assembly or a reduced pressure principle backflow preventer – depending on the degree of the site hazard.

With proper maintenance and annual testing, backflow prevention assemblies have been known to last for many years.

A potential hazard is defined as any possibility of pollutants, contaminants, and system or plumbing hazards. For example, fire protection systems, irrigation systems, gasoline refineries and stations, restaurants, hospitals and manufacturers.

No. SAWS Backflow Prevention Section will continue to review all permits and utility drawings to ensure compliance with backflow prevention requirements, and will continue to oversee the installation and testing of the assemblies.

Yes. SAWS Backflow Prevention Section will continue to mail out a test due notice to all customers with a backflow prevention assembly. Testing requirements must be completed within 30 days of the test due notice.