Backflow preventer and drip irrigation

If I understand things correctly backflow preventers are designed to prevent a vacuum from pulling water (and whatever else) back into the water supply. With an irrigation timer and a supply valve that is not shut off due to being on said timer are backflow preventers necessary? Does the timer itself not serve as a backflow preventer?

I was reworking some of my irrigation this morning and noticed that one of the backflow preventers was spraying water. I removed it and hooked everything else back up and there was no more leaking/spraying. Just curious as to how necessary they are when used downstream of an irrigation timer.



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I’m sorry I can’t answer your question, but I cannot pass the opportunity to express my frustration with some water company policies regarding back-flow preventers. I have a long running fight with the utility that provides water to the City I work for. I understand that there are places where backflow preventers absolutely make sense and should be required. Any place that has chemicals or other contaminants that could be problematic if they got into the water system should have backflow preventers. But our utility company passed a new requirement forcing every government or business to install a backflow preventer. So, for example, our small public library that has nothing but 2 bathrooms with 2 sinks and commodes in each had to spend over $1,000 to install a backflow preventer. In many cases, these buildings have concrete floors so you either have to bust them up or install the backflow preventer outside-in which case you have to build a special box with a heater to prevent freezing. Worse yet, the water company has to come inspect all backflow preventers once a year, and I’d say 25% of the time they say it failed the test and we have to hire a plumber for $500- to come replace it. All this to prevent what? What is in an insurance office, for example, that is going to get into the water system and be dangerous. If your answer is sewage, you should know they already had a law requiring water lines be at least 10 feet from any water line. Also, what are the odds that something is going to get into a pressurized water line? I know, there is always a chance that sewer could leak (1st event) then run 10 feet over to a water line (2ed event), then at the same time there could be a ruptured waterline at some other location (event #3) that would result in the water line loosing pressure, then the water line has to have a hole or leak at the same location as where the sewer has run over to it at (event #4). If all 4 of those things happen, it is possible that sewer could get in the waterline. But this could also happen -and is more likely-on the other side of the back flow preventers, rather than in the building.

I am not saying it is impossible for a small office or a library to have a long string of events that could result in something bad getting into the water. But the risk is so low I just don’t think its fair to make them all install expensive backflow preventers and have them inspected and be a constant problem. I also acknowledge some of you may disagree and that is ok, but to me, this is just another case of utilities with monopolies being able to do anything they want to. I’m sure the new income stream they get from the money they charge to inspect newly installed BF preventers and the annual inspection has nothing to do with their decision to require them everywhere. And I have a bridge to sell if you believe that!!! haha

Matt, I’m sorry to get on my soapbox on your thread, but it is related and I’m interested to see what folks say to both our comments/questions.

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If I am not mistaken you are required to have one. Our situation is a little different from yours because ours is in the house to prevent any possibility of our well being hooked into our household water system and feeding the city water lines, but the principle is the same: protecting the municipal water supply.

I appreciate @thecityman 's point about the expensive, unnecessary installations, but on irrigation systmes I can see the need, even with the timer.

Interestingly, Kevin, the people that inspect our unit every year ($50 a pop) are independents, not hired by the water company. Our unit is a 3/4" Wells, and fails every year on the first test, passes on the second. One year the tech dismantled our valve and installed the kit I had on hand at no extra charge. The 3/4" valves will almost always fail on first test, but I’m told the 1" valves almost never do.

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I should have said I would agree with having one on an irrigation system- absolutely. There are fertilizers and standing water (at times) and lots of other good reasons. I’m also surprised independent companies do your inspections- I still would be curious if some of that money goes back to the water utility. If not, it erodes a bit of my cynicism- at least for your utility company but not for my own. Mine charges $75 for the inspection and hired people in-house to do them. So far ours doesn’t require them for single family residences, but I am confident that will be the next step! Anyway, I know they can be a good thing and I’m probably being overly critical, but our small local government had to spend a small fortune to put them in every single government building, as well as paying for inspections, all for locations that I feel just don’t need them and haven’t had them for the last 100 years! Oh well, maybe that’s just progress!

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It does make a person wonder, doesn’t it?

I can understand codes changing and being updated to reflect changing needs (increased population densities and better understanding of risks, for example) but I’m in favor of grandfathering some of this stuff. We have a city air pollution ordinance in place that prohibits the new installation of most wood-burning stoves, so if a house is sold the stove cannot be used by the purchaser. But people who have built their lives around the old technology don’t have to suddenly install central heating, etc. Heck, this area didn’t even have natural gas lines at all until 1959! Our house still has the original coal and sawdust chutes and some of the original knob-and-tube wiring.