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You do not necessarily need an additional backflow preventor as your main line to your house should contain one at the connection source from the city. On my installs I always install a check valve for the portion of the line supplying the sprinkler system, just as a precautionary to keep "dirty" water from backing into the main line to the house. The check valve only opens up to allow water to the sprinkler system when the system is on.

First let me say sorry for taking so long trying to post to this question. I tried to get in, but my old password wasn't working.

When I requested a new password, it took me a few days before I relalized the link I was emailed to follow did not include the ".com" in "sprinklertalk.com". Obviously there are a few bugs to shake out of the new forum here.

Quoted from "kjones911"

You do not necessarily need an additional backflow preventor as your main line to your house should contain one at the connection source from the city. On my installs I always install a check valve for the portion of the line supplying the sprinkler system, just as a precautionary to keep "dirty" water from backing into the main line to the house. The check valve only opens up to allow water to the sprinkler system when the system is on.

#1. You can't assume there is even a check valve between the mainline to the house and the mainline to the irrigation. After all, a properly installed system SHOULD contain a back flow preventer.

#2. A Check value is NOT a back flow preventer.

The problem with a simple check value is that it can easily get stuck "open" if there is any trash in the lines and allow water to back flow. And I can tell you from experience that there is trash in the lines, even on city water. Based on advice from www.irrigationtutorials.com, I installed a fine mesh filter at the start of my irrigation system. The 1st year of use, I found a 1/2" long piece of something that looked like a part of a tooth pick (ON CITY WATER in a city that is considered to have very good water quality).

The other problem with a check valve (or even a double check) is that there is no way to test them to insure they are working.

What you really need is either a double check (DC) backflow preventer (it's basically just two check valves, but it includes test cocks so you can prove it is still working), Reduced Pressure Zone (RPZ), Pressure Vacuum Breaker (PVB) or Anti-siphon valves.

If you want to insure your instalation is legal, you need to check with your local building codes department and determine which ones meet codes in your area. Some places simply state any sort of back-flow preventer, others will go so far as to specify a part number (i.e. type, manufacture, and part) that must be used to meet code.

Here's a direct link for more information at the web site I mentioned before. It's got lots of great information and referened my many on these boards. http://www.irrigationtutorials.com/sprinkler08.htm

Great Comment.

Dan Todd

Quoted from "jenn"

... Is it absolutely neccesary to have a backflow preventor? Also, shouldn't the inspector have noticed this issue??? Lastly, just how pricey is this sort of thing to remedy? ...

OK, I see that my previous response did not address these specific questiong:

Is it absolutely necessary? Well, a backflow preventer is sort of like a circuit breaker. If you replace the circuit breaker with a bare piece of copper, will the lights still work? Yes. Will it protect the circuit from causing a fire during an electrical short? Of course not. The Backflow preventer is sort of the same thing for your irrigation. The irrigation system will work just fine without it. But you put yourself at risk from contaminating your home water. Basically, without a backflow preventer, things like fertilizer you spread on the lawn can find it's way back into your home through the irrigation system. You would think the control valve would prevent this from happening, but that is about like saying the light switch should protect the circuit from causing a fire.

Shouldn't the inspector have noticed this? Ideally, yes. But there are many reason this could have been missed. For one, you MIGHT be in an area that there are no building code that legally require you to have a back-flow. Then there is the obvious possibility of simple oversight. Then you start getting into the issues of some home inspectors really are not qualified to do the job. It's quite possible that you got a home inspector that doesn't really know anything about irrigation systems. I've personally know people that had so many problems with a house after they moved into it, they got involved in a major lawsuit with the inspector. Then there is the general truth that many home inspectors will not have the buyer's true interest at heart. Many of these inspectors are hired from referrals by real-estate agents. If an inspector gets a reputation of killing sales because they find too many (even legitimate) things wrong, the agents will quit referring them.

How Pricey? Depends upon how much of the work you can do yourself. At a minimum, you can try to locate and dig up and expose the pipe at the point where the water lines split (to house and irrigation). But after that, it depends upon local codes. In some areas, it's required that a certified plumber install back-flows. Other places, it's allowed to be a do-it-yourself job. So if you can do all the work yourself, the parts should cost around $100. If you only need a plumber to install and you're going to do all the digging, I would expect the plumber should be able to do the job in less than 2 hours (unless he has to do more digging for you) and could cost as little as an additional $200. If the plumber has to dig up the lines, install the backflow, install a valve box, and replace all the soil, I could see it being $1,000.