Lawn Sprinkler System 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 withstand .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 back-pressure.
3. Are check valves ever 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 with the loss of water pressure.
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, from irrigation supply houses and over the Internet?
Yes! The injection units are becoming more and more prevalent. We experienced a situation in San Antonio where a ‘contractor’ was replacing the backflow prevention assemblies with aspirator type chemical injection units. This was not discovered until a vigilant and concerned citizen contacted the water department.
7. How does an enforcement agency know when a chemical unit has been installed?
Without a permitting process and continuous monitoring of backflow prevention assemblies through periodic testing and maintenance, there is absolutely no control over these cross connection hazards. Who is willing to have their neighbor install a chemical injection unit without backflow protection?
8. Along with the development of water conservation measures, has evolved irrigation systems utilizing water from various sources, e.g., spray aerobic, gray water, cisterns, recycle water, etc.
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 that’s supplied from the city’s potable water been inter-connected to a well to boost water pressure, or inter-connected to an onsite auxiliary water supply?
9. How does a person determine if a backflow situation has occurred with a lawn sprinkler system and the potable water is contaminated?
A backflow situation from a lawn sprinkler system can be very difficult and may be virtually impossible to detect. Contamination from cross connections and backflow situations will routinely go undetected 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. Why is this, with water departments having numerous main breaks and the water turned off for various other reasons? Are there no irrigation systems on at the time of the loss of water pressure? Are all check valves closed tight? Are irrigation control valves preventing backflow when they can only withstand .5 psi back-pressure??
The following will 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. The cheaper, unapproved model does not have backflow protection, or plumbing code approval.
With the loss of water pressure on the unapproved model, water from the commode tank can drain into the potable water system, e.g., icemaker, facilities drinking water, and in some cases back into the city’s potable water system. Water from the commode tank will only be discovered if the facility is utilizing a colored commode additive, e.g., blue boy, and dilution has not affected the ability to visually observe the polluted water. The water coming from a faucet and/or the ice will be colored. The last time we checked there were numerous commode additives on the market with several labeled as toxic, and one advertised as having no color or odor. So, with the lawn sprinkler system – how do you determine if a backflow situation has occurred?
Although the commode ball cock is against plumbing codes, it is generally sold throughout the United States and will only be removed from the store shelves when the supply store is confronted by an enforcement agency.
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 and is the backflow protection only inspected when new and never looked at again?? When was the last time your lawn sprinkler system’s backflow prevention assembly was tested??
Does the average citizen or politician that argues 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, inter-connected their potable water irrigation system to their on-site auxiliary water system, e.g., well, spray aerobic, gray water system, cistern, etc., removed the checks from the backflow preventer, modified the terrain, etc.? How many lawn sprinkler systems are being drained into the public water supply every time pressure is lost — again – .5 psig back-pressure? Basically, is the backflow protection appropriate for the hazard and performing as designed? Are Codes Being Enforced? Is the potable water being protected?