Lawn Sprinkler Systems and Backflow Protection

Through the years we’ve heard from some that lawn sprinkler systems are not a cross connection hazard and all that’s necessary is minimal backflow protection with no periodic testing or maintenance.  Listed below are a few considerations and questions that might be asked about the actual or potential contamination hazards associated with lawn sprinkler systems before calling a lawn sprinkler system a no or low cross connection hazard, that doesn’t need to be monitored. Did you know - Irrigation Control Valves only hold back .5 psig back-pressure! What happens if the backflow protection isn't working as designed or if the backflow preventer is not  installed?

1.      Are water pressures always constant and is flow always in the direction intended?

No. Backflow occurs every time water pressure is lost and anytime a piece of equipment or process is connected to the potable water supply that creates higher pressure than that supplied by the water department. Water departments continuously experience main breaks that involve turning the water off to numerous facilities. Additionally, high demands on either the public water system or a facility's internal water system create pressure drops and backflow situations.  

2.   Do check valves ever fail due to debris in the line? 

Check valves and shut-off valves can easily become fouled from debris in the water line, thereby allowing backflow to occur through leaking checks or shut-off valves. In most instances, contamination problems from cross connections and backflow situations are through leaking check valves and/or shut-off valves. Lawn sprinkler solenoid valves can withstand only .5 psi of back-pressure.

 3.   Can check valves be destroyed due to water hammer created by quick closing valves downstream of the backflow preventer?

Backflow prevention assembly testers routinely find destroyed check valves on lawn sprinkler systems due to water hammer (extreme high back-pressure). The destroyed checks will only be discovered through periodic testing and maintenance programs.

4.   Are backflow prevention assemblies or other factors ever modified that affect the backflow preventer?  

There are any number of things that can affect the backflow preventer’s ability to prevent backflow, e.g., terrain modifications, addition of chemical injection units that can create back-pressure, by-pass arrangements, check valves removed, etc. We have seen check valves within backflow prevention assemblies removed just to increase the water pressure, giving little thought to the water around the sprinkler head (fecal matter – chemicals) being siphoned into the potable water system.

5.    Does the average citizen know that city water pressure does not have to be lost for back-siphonage to occur?

One of the main causes of backflow is the loss of water pressure due to an aspirator affect. The water pressure at the water main can be 90 or a 100 psi and high demand on the water main or a facility’s internal water line can create such a high volume flow that a vacuum or partial vacuum will be created on any taps or tees off the line which will contribute to both a back-pressure and  back-siphonage condition. Water contamination in these situations is very difficult to detect due to the dilution factor.   

6.   Are chemical injection units for lawn sprinkler systems available, either from irrigation supply houses or the Internet? 

Yes. The injection units are becoming more and more prevalent. We experienced a situation in San Antonio where a person had been replacing the backflow prevention assembly on irrigation systems with aspirator type chemical injection units. This was only discovered due to a vigilant and concerned citizen contacting the water department.

7.   How does an enforcement agency know when a chemical unit has been installed?

If there is no permitting process and a lack of continuous monitoring of  backflow prevention assemblies through periodic testing and maintenance,  there is absolutely no control over these cross connection hazards. Who would know if your neighbor installs a chemical injection unit directly off the city water supply without backflow protection?

8.   With the development of water conservation measures has evolved irrigation systems utilizing water from various sources. Examples: spray aerobic, gray water systems, cisterns, recycle water.

How do you or the local enforcement agency know when these systems are installed and are they being continuously monitored and controlled? Has the lawn sprinkler system supplied from the city’s potable water supply been interconnected to a well for the purpose of boosting pressure or supplying water to the sprinkler system when the auxiliary system is down?

9.   How would a person determine if a backflow situation had occurred with a lawn sprinkler system resulting in the potable water being contaminated?

A backflow situation from a lawn sprinkler system can be very difficult and sometimes impossible to detect. Contamination from cross connections and backflow situations will routinely go undetected in the water main due to dilution and will only be discovered when the concentration is high enough to create a taste, color or odor problem and/or when illnesses are reported. Very few backflow incidents have been documented involving lawn irrigation systems. Does this mean backflow is not occurring? No. Water departments routinely shut down water mains throughout the year due to main break repairs, maintenance issues or other reasons. Water pressures are always changing. One misconception: an irrigation system has to be operating at the time of pressure loss for backflow to occur. This is false. Irrigation control valves only hold back .5 psi of backpressure and are not to be considered backflow preventers. Any low heads under water upon closing can result in fertilizer and/or fecal matter flowing back into the potable water. 

The following may assist in understanding cross connections, contamination, backflow and the dilution factor:

Unapproved commode tank filler valves (commode ball cocks) are an easy way to explain the physical factor (color, taste and/or odor) necessary to detect a contamination problem.  There are two types of commode tank filler valves on the market with one having a built in backflow preventer and the cheaper,  unapproved model not having backflow protection and plumbing code approval.

Although the commode ball cock is against plumbing codes, it is generally sold throughout the United States and will only be removed from the hardware shelves when the supply store is notified by the enforcement agency.

With the loss of water pressure on the unapproved model having no vacuum breaker, water from the commode tank will drain into the potable water system. Water from the commode tank may only be discovered in other areas of the home if the commode has a colored additive. This is when blue water is reported coming from bathroom faucets, the ice maker in the kitchen and other areas. The last time we checked there were numerous commode additives on the market with several labeled toxic. One of the toxic brands advertises no color or odor. So, back to the lawn sprinkler system, how do you determine if a backflow situation has occurred? Dilution and no color are two factors that may play a role in not knowing.

10.    Why do national plumbing codes and all national water purveyor guidelines consider lawn sprinkler systems a high risk cross connection hazard?  

National water codes and guidelines call for approved backflow protection on all lawn sprinkler systems and the backflow protection to be tested and maintained in a working condition. All national codes and water purveyor guidelines consider lawn sprinkler systems a high cross connection hazard. Ask yourself and your local water purveyor, plumbing inspection department and politician how is this enforcement achieved. Are lawn sprinkler systems being continuously monitored or is the backflow protection only inspected when new and never looked at again. One question may be, when was your lawn sprinkler system’s backflow prevention assembly last tested for proper working condition.

Does the average citizen or politician arguing against the necessity for viable backflow protection on lawn sprinkler systems, including periodic testing and maintenance, really understand what they are saying?  Has any thought been given to whether or not their neighbor has installed a chemical injection unit on their irrigation system, interconnected the potable water irrigation system to their on-site auxiliary water system such as a well, spray aerobic, gray water system, cistern, etc. Shouldn't periodic testing be required to ensure check valves haven't been removed from the backflow preventer, to detect terrain modifications or whole backflow assembly removal. Is the backflow protection appropriate for the hazard and performing as designed? Are codes being enforced? Is the potable water being protected?