Backflow is the undesirable reversal of water flow in a water distribution system. Water distribution systems are designed for the water flowing in one direction, from the distribution system to the many various points of use. Hydraulic conditions can and do exist within the system that may deviate from the "normal" conditions, causing water to flow in the opposite direction.

Causes of Backflow

Backflow is caused by either a drop in pressure in the water supply (back-siphonage) or an increase in the water pressure (backpressure).

• Back-siphonage 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 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 businesses 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.

• 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 back into the water supply.

Potential Backflow Hazards

  • In-ground lawn sprinklers
  • In-ground swimming pools
  • Hose Bibs/Outside Spigots
  • Boilers
  • Solar heating
  • Decorative ponds
  • Fire protection systems (including fire lines and fire sprinkler systems)
  • Many other commercial uses

How to Help Prevent Backflow

  • Maintain and annually inspect in-ground lawn sprinkler systems and other backflow devices.
  • Never submerge a hose in buckets, pools, tubs or sinks.
  • Always keep the end of the hose clear of possible contaminants.
  • Don’t use spray attachments, especially those with fertilizers or chemicals, without a backflow prevention device.
  • If an outdoor faucet doesn’t have a built-in anti-siphon valve, an inexpensive screw-on backflow­­ prevention device (hose bib vacuum breaker) can be purchased and installed. Be sure to periodically inspect these devices to ensure they are working properly and replace them if needed.

Who is Required to Have a Backflow Device and Your Responsibilities

Water customers with a known or potential cross-connection (a connection between our drinking water system and another substance or source) are required by state and local laws and regulations to install a backflow prevention assembly and have it inspected and tested annually by a certified backflow tester with a current Lee’s Summit business license. Yearly testing is necessary to ensure the assembly is operating properly in order to protect our water system from possible contamination. Find licensed backflow testers here.

You should never use an in-ground lawn sprinkler without having a properly tested and functioning backflow assembly.

Lee’s Summit Water Utilities mails customers with registered lawn sprinkler systems a testing notice every spring to remind citizens/businesses of their test date. If you have an in-ground lawn sprinkler and DO NOT receive a testing notice (or have not in the past), please have your assembly inspected before use and ensure your backflow test report is submitted to us at

What laws require me to have a backflow device? 
The EPA Safe Drinking Water Act
Missouri Code of State Regulations 60-11.010
Lee's Summit's Backflow Prevention Ordinance (Chapter 32, Article III of the Code of Ordinances)
Lee's Summit's Design and Construction Manual

What is the technical definition of 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. 

Backflow Prevention Program

Lee's Summit Water Utilities maintains records on each backflow device. The utility mails customers with registered backflow devices a testing notice every spring to remind them to complete their backflow testing by the due date listed on the notice.. A list of certified testers will be enclosed with the reminder letter. It is up to the backflow device owner to contact a certified backflow assembly tester. 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 and submit the report to Lee's Summit Water Utilities on behalf of the customer. Customers will need to confirm with the tester whether the report has been submitted and received by Lee's Summit Water Utilities. 

According to the City ordinance 32.143 (in accordance with Federal and State regulations), if an owner does not perform the testing annually, it is the Water Utilities' right to terminate water service. Annual testing ensures the greatest protection of the City's public potable water system. Verification of the backflow preventer's accuracy is essential.  The backflow assembly test reports can be emailed to, mailed, or dropped off to Lee's Summit Water Utilities.

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 backward 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 also fail.
  • A hose bib vacuum breaker should be installed on all hose bibs without anti-siphon 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 anti-siphon hose bib already has a vacuum breaker built-in.

Resources for Additional Backflow Questions 

For additional backflow questions or concerns contact Lee's Summit Water Utilities at 816.969.1900 or email us at