What is backflow?
What causes backflow?
Potential backflow hazards
What is a backflow assembly?
What is a cross connection?
Who is required to have a backflow device?
Why does a backflow device have to be tested Annually?
Backflow Prevention Links
What is Backflow?
The Water Utilities Department strives to provide reliable and safe drinking water to our community. Many of us, however, take for granted that we can fill our glasses with safe drinking water everyday. Drinking water distribution systems are designed with the intention of the water flowing in one direction, from the distribution system to the many various points of use. Unfortunately, hydraulic conditions can and do exist within the system that may deviate from the "normal" conditions, causing water to flow in the opposite direction. This undesirable reversal of flow is called backflow.
What Causes Backflow?
There are two types of backflow: backpressure and backsiphonage.
Backpressure is caused by a downstream increase in pressure to a point that is greater than the supply pressure. An example would be a connection to a boiler for heating purposes. As the water is heated, it expands and increases the pressure in the boiler. The pressure in the boiler can reach a point where it is higher than the pressure of the water supply line. If this occurs, the water from the boiler will push back, or flow, into the water supply as it looks for space to relieve the pressure. Another example would be any situation where a water connection is made to a pump to increase water pressure. Enough pressure can be created downstream from the pump, that it will surpass the pressure in the water supply connection and flow backwards into the water supply.
Backsiphonage is caused by a drop in supply pressure where a partial vacuum or negative pressure is created that siphons water or liquids into the water supply. It is similar to drinking water through a straw. A good example is of a water hose submerged in a bucket to mix up fertilizer or pesticide. If a water main were to break down the street and there was a sudden drop in supply pressure, water from nearby homes and business could be siphoned into the drinking water system, including the fertilizer or pesticide in the bucket. After the break is fixed, someone could go to fill up their glass at the tap and unknowingly drink water contaminated with fertilizer or pesticide.
Potential Backflow Hazards:
- In ground lawn sprinklers
- In ground swimming pools
- Hose Bibs
- Photo Dark Rooms
- Solar Heating
- Decorative Ponds
- Fire Protection Systems (including fire lines and fire sprinkler systems)
- Many other Commercial uses
What is a Backflow Prevention Assembly?
A backflow prevention assembly protects drinking water from contamination through cross-connections via check valves, air relief valves or a combination of both. There are several different types of backflow prevention assemblies.
A double check valve assembly (DCV) contains two spring loaded check valves that are held open by normal water pressure. Should a backflow situation occur and the water pressure drops, the springs will close the two check valves that are normally held open by normal water pressure. These closed check valves keep water from flowing backwards into the water supply. A DCV protects against low hazard cross connections.
A reduced pressure zone backflow assembly (RPZ) contains two spring loaded check valves like the DCV but also contains an air relief valve for an added level of protection for high hazard cross connections. If the first check valve should fail when a backflow situation occurs, then the air relief valve will open allowing the backflow water to discharge from the device instead of backflowing into the water supply. The second check valve provides an additional level of protection if the air relief valve should fail also.
A hose bib vacuum breaker should be installed on all hose bibs without antisiphon devices already built in. A hose bib vacuum breaker contains an air relief valve that will discharge water that tries to backflow into the private water supply. An antisiphon hose bib (pictured to the right) already has a vacuum breaker built in.
What is a Cross-Connection?
A cross-connection is an unprotected actual or potential connection between a potable water system used to supply water for drinking purposes and any source or system containing unapproved water or a substance that is not or cannot be approved as safe, wholesome, and potable. By-pass arrangements, jumper connections, removable sections, swivel or changeover devices, or other devices through which backflow could occur, are considered to be cross-connections.
Who is Required to Have a Backflow Device?
In accordance with The EPA Safe Drinking Water Act and Missouri Code of State Regulations 60-11.010 the City developed a Backflow Prevention Ordinance (Chapter 32, Article III of the Code of Ordinances) and standards in the Design and Construction Manual in support of these laws. The purpose of the ordinance and standards is to protect the public potable water supply from possible contamination by backflow through cross-connections. All water customers with known or potential cross connections are required to install a backflow prevention assembly and have it tested annually.
Why Does the Backflow Device Have to be Tested Annually?
In accordance with Federal and State laws, the City requires each backflow prevention assembly to be tested annually. This testing ensures the greatest protection of the City’s public potable water supply. Verification of the backflow preventers accuracy is essential. The City’s Backflow Coordinator maintains files on each backflow device. Letters are sent annually reminding citizens/businesses of their test date. It is then up to the backflow device owner to contact a licensed and certified backflow assembly tester. A list of licensed and certified testers is also enclosed with the reminder letter. The owner then has approximately 30 days to schedule the testing. The tester will complete the Backflow Prevention Assembly Test Data and Maintenance Report that indicates whether or not the backflow assembly passed or failed in several areas. The tester will return the report to the Backflow Coordinator, however, it is a good idea for the owner to verify that the report has been received. The Backflow Coordinator will issue several warnings if this report is not received in a timely manner. According to City ordinance (in accordance with state regulations), if an owner does not perform the testing annually, it is the Water Utilities right to terminate water service in order to protect the public water system. The backflow assembly test report can be mailed to the address indicated on the form or faxed to (816) 969-1935.
Backflow Prevention Links
Missouri Department of Natural Resources Backflow Prevention Website
U.S. Environmental Protection Agency (EPA) Cross-Connection Control
American Backflow Prevention Association (ABPA)
American Society of Sanitary Engineering (ASSE)
Any additional questions or concerns can be directed to the City's Backflow Coordinator at (816) 969-1930 or emailed to firstname.lastname@example.org.