# Are backflow prevention devices necessary on irrigation systems?



## Tom Struble (Dec 29, 2008)

well if its just your families health and wefare i'd say screwem:thumbsup:


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## downunder (Jun 13, 2008)

From Widipedia Reduced Pressure Zone Device:

"An example of where backflow would harm the water supply is the use of well washing devices inside underground sewerage pumping stations. At times untreated sewerage may contain a variety of harmful gases that will effectively break down and deteriorate concrete wells, hence well washers are utilised to spray water and wash down contaminated concrete walls of a well. All well washers are installed with RPZ Devices in case a pumping station breaks down, and the *sewerage level rises above the well washer causing backflow down the water supply line.*" Bold emphasis mine.

Note that a key factor is that the sewerage level rises above the well washer. For any system to have backflow, there must be a way for the contaminant to be sucked back into the water supply, as is described here. So for one thing, unless one has some part of an irrigation line submerged into another source, I just don't see how contamination can happen.


*Backflow prevention device*

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A *backflow prevention assembly* is used to protect water supplies from contamination or pollution.
 
In this situation, dirty water from the hillside pool will _back siphon_ or _back flow_ down the hosepipe and into the clean water tank. To prevent this from happening, the house's external tap should be fitted with a backflow prevention device.


In water supply systems, water is normally maintained at a significant pressure to enable water to flow from the tap, shower etc. When pressure fails or is reduced as may happen if a water main bursts, pipes freeze or there is unexpectedly high demand on the water system, the pressure in the pipe may be reduced and may allow contaminated water from the ground, from storage of from other sources to be drawn into the system. To prevent such an occurrence, many regulatory regimes require there to be an air gap or mechanical backflow prevention assembly between the delivery point of mains water and local storage or use [1] Where submerged mains inflow is permitted a backflow prevention assembly is required. In this way the backflow prevention assembly protects the potable water system from contamination hazards which can be severe. There are over 10,000 reported cases of backflow contamination each year. Some cases can be fatal.
In many countries where regulations allow for the possibility of backflow , Approved backflow prevention assemblies are required by law and must be installed in accordance with plumbing or building codes.
A typical backflow assembly has test cocks and shut-off valves and must be tested each year, if relocated or repaired, and when installed.
In the United States, the Environmental Protection Agency (EPA) holds local water suppliers responsible for maintaining a certain amount of purity in potable water systems. Many states and/or local municipalities require annual testing of backflow prevention assemblies. A check valve is a common form of backflow prevention. In most cases, the law requires a double-detector check, an RP device or an air gap when backflow prevention is mandated.
The simplest, and most effective way to provide backflow prevention is to provide an air gap. An air gap is simply a space between any device that opens to a plumbing system (like a valve or faucet) and any place where water can collect or pool.


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## jasoninct (Oct 10, 2010)

wether a backflow preventer is needed should be dictated by local building code. 

Here in CT backflow preventers are required for any permanently connected irrigation system. If an irrigation system is connected to a sill cock it is not considdered a permanent connection.


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## FourIsWaltz (Oct 10, 2010)

If you lose pressure in the house, and you have tight soil, a seasonal high water table, or you just watered, you can get shallow ground water flowing in and mixing with the house supply. Then the pressure comes back on and next time you get a drink from the tap, you're sipping poorly filtered dog turd water from the yard. Dirt tea. All kinds of interesting soil bacteria. Yum.

A check valve can be cheap (but where they are required, they're suddenly all kinds of expensive!) so it makes sense to put one on. It's low cost and low effort to reduce the likelihood of a low risk bad outcome (adults could spend a week on the toilet, immune-compromised, old, or young people could die).


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## downunder (Jun 13, 2008)

FourIsWaltz,
I have a default philosophy of basically, "What's the worse that can happen between choice A and choice B?" So I agree with these devices being low effort, and to some degree low cost. Yes, it seems like when they are required things suddenly get expensive. However, I think your first point has a lot of "ifs" in it and so maybe I should say, "What's the reasonably worse...?"

Jason's point is an example of my problem with the carte blanche recommendations for backflow preventers. Yes for a permanent installation and no for a sillcock connection. I just can't believe that water knows what it is connected to- a system is either potentially dangerouss or not. Unless someone can explain how it matters which method of supply is used. 


> Then the pressure comes back on and next time you get a drink from the tap, you're sipping poorly filtered dog turd water from the yard. Dirt tea. All kinds of interesting soil bacteria. Yum.


Maybe filters should be required instead. That way, instead of just protecting you from you, you could protect yourself from all sources of contamination.

As far as local codes are concerned, I would never suggest to not use any required safety device or procedure. But codes cannot change the laws of physics. Just because it's code doesn't mean that it is necessary; rather it just seemed like a good idea to someone. I've just seen so many instances of "code" or something required that really just boiled down to common sense, laziness, stupidity, etc. 

For instance, I just bought a new lawn mower with an RIO (reverse implement operation) switch. The idea is that you have to press this switch (something else to distract you in my opinion) and hold it in while you shift into reverse. You reach forward and look for a switch AND turn around and look behind you AT THE SAME TIME. This is supposed to make you look behind you before backing up with the blades engaged. I don't see how. This came about because a mother was not watching a two year old in the house in California and the child went into the yard. Dad was mowing the lawn and he backed over the child's foot while he backed up with the blades engaged because he did not know the child was in the yard. So now every lawn mower (except ZTR) has this switch installed.

And I know of a small town that passed an ordinance that everyone working in restaurants with alcohol had to have a "server's ID." In reality, this town did not want a certain club franchise coming to town so they passed a set of "qualifications" for someone to work in restaurants. Now everone is safe!:laughing:


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## FourIsWaltz (Oct 10, 2010)

We are stuck with a representative democracy in a federal system, and that comes with some noise and idiosyncrasies in the laws, rules, and regulations. If you think the building codes are bad (I do) try driving across three states with a rifle.

Even if it wasn't required, I'd drop a check valve in where there was a reasonable possibility of backflow. Certainly on a permanently connected irrigation system, and for one that hooked to the hose bib, I'd just leave one on the hose bib, and while at the hardware store, pick one up to put on a slop sink that could have a hose attached.

Yes, the chain of "ifs" to get from a normally functioning irrigation system to a dead mother-in-law is rather long, but none of those things is unlikely on its own. The probability of all of them happening together is small, but still far enough from zero.

I come down on the side of reasonable response to risk. With a check valve, the risk of harm is small, but the cost and effort to prevent that risk is also small. It just makes sense to go to a very small amount of effort to protect from a very small risk of serious harm.


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## downunder (Jun 13, 2008)

I was in Lowe's today and walked over the plumbing aisle. The RPZ's are $179. The double check valves are $99.

Notwithstanding the above, what do you consider a check valve? Just to get on the same page, do you mean a vacuum breaker, anti-siphon valve, or what?


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## SPS-1 (Oct 21, 2008)

FourIsWaltz said:


> If you lose pressure in the house, and you have tight soil, a seasonal high water table, or you just watered, you can get shallow ground water flowing in and mixing with the house supply.


... one more "if"...... you solenoid valve on your irrigation system has to fail at the same time, or it opens on timer while you have no pressure


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## downunder (Jun 13, 2008)

SPS,
Sorry, but I don't understand your comment.


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## SPS-1 (Oct 21, 2008)

There is going to be an electrically operated solenoid valve for each zone of the irrigation system. The valve needs to be "open" in order for the system to back-flow.


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## downunder (Jun 13, 2008)

> ... one more "if"...... you solenoid valve on your irrigation system has to fail at the same time, or it opens on timer while you have no pressure





> There is going to be an electrically operated solenoid valve for each zone of the irrigation system. The valve needs to be "open" in order for the system to back-flow.


Do these mean the same thing? I don't understand the point about the solenoid has to fail at the same time.

I think most of understand how an irrigation system works. The valve does not have to "be open" to provide a means of pollutants to enter. This may be because it is open, or may be because it is faulty. Or there may be a leak through a broken supply pipe. And you cannot have a backflow with no pressure. You have to have a negative pressure, otherwise the pollutants will just sit there, like a car sitting on level ground. It is usually a good idea to set the parking brake, but absent gravity or some extraneous force acting upon it, the car will not move. 
Did you have something to contribute as to why or why not use a backflow preventer?


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## FourIsWaltz (Oct 10, 2010)

downunder said:


> ...what do you consider a check valve? Just to get on the same page, do you mean a vacuum breaker, anti-siphon valve, or what?


I could understand the water company wanting an RPZ between their supply and a resident's aux well, but for an irrigation setup an RPZ is overkill. A single check, a vacuum breaker, or an antisiphon would run between $4 and $20. With the long string of IFs already discussed, a little extra insurance is enough. (Again with the risk. $20 to reduce risk makes sense to me. $200 to reduce risk--that buys a lot of immodium.)


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## downunder (Jun 13, 2008)

> I could understand the water company wanting an RPZ between their supply and a resident's aux well, but for an irrigation setup an RPZ is overkill.


A. Sorry if I gave that impression. I do not have a well and the meter does not have an RPZ, just a meter backflow preventer.
B. Frankly, an RPZ is the only really safe device to use on an irrigation system. Which is somewhat my point in this thread. I can see a $20 safety valve. In the big picture, it's not much to add to the already several hundred dollars' worth of system. On the other hand, do you think they would provide a false sense of security. I tend to think they give an 80% degree of protection against a 99% probably safe anyway system. 

Like when I rebuild engines; I NEVER put an old oil pump back in and usually replace the timing chain also. If I spend that much time rebuilding an engine, I don't want it to come apart because of a $20 (well, they used to be!:thumbup oil pump. If the timing gear goes, the engine just quits. If the oil pump fails, the whole engine is gone.

Oh well, thanks to all for the input. If local code requires it, then by all means there is no question. Put at least whay they tell you. I'm still not convinced that these devices are the "got to" that some would suggest, but maybe I'm not quite as much against them as I was.

FWIW- I was in public safety for nearly 30 years, so I'm not against precaution at all. But what would everyone think if police officers put you on the ground with shotguns just for running a stop sign. I could say that it's possible that you just robbed a bank, so I was just being careful. Result A is that you get your feelings hurt. Result B is that I get killed. But somewhere in there is a reasonable safety measure that protects with an acceptable degree of risk. Which is my point here. I see the remote possibility of contamination from most irrigation systems as an acceptable risk. Like every car you meet on a two lane road. It is possible that the next car you meet could blow a tire, not be paying attention, or have a heart attack going down the road. But you have faith and trust that they will pass by safely just inches away meeting you head-on. I did stop a driver one time who immediately placed his hands on the roof of the car. But he was from the middle east. No offense to anyone with that account I hope. And backdraft is backdraft in a fire. It doesn't care who you are or what the codes say, it is all about physical science. And I am much more cautious now when performing CPR or running a stabbing call.


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