Irrigation Safety 101: Why Backflow?

You must have a backflow preventer on your irrigation system. In most places this is the law, everywhere else it's just the smart thing to do. Almost everywhere the local authorities will dictate that certain types of backflow preventers may not be used with irrigation systems because they do not provide adequate protection. In some cases, the authorities will dictate the exact type of backflow preventer you MUST use. You may hear or see the term "Cross-Connection Control" used, this essentially is referring to backflow prevention.

Why do you need a backflow preventer? All irrigation systems contain a chemical called dihydrogen monoxide. This odorless, tasteless chemical is known to be deadly if inhaled and has killed millions of people. OK, before you flame me, dihydrogen monoxide is, of course, the scientific name for ordinary water (h2o). Which points out that you have to be really careful about what you read and believe on the Internet. Unfortunately when it comes to backflow preventers there is a lot of questionable, and sometimes completely wrong, information. So what's the deal with backflow prevention? Is it really necessary? The answer is yes!
Your landscape has all kinds of nasty things in it that will make you sick or worse if you drink them. Thus irrigation water is considered a contaminant (creates a health hazard) rather than just a pollutant (is objectionable in color or odor). What's in irrigation water? How about toxic chemicals (fertilizers, pesticides, etc.) and animal waste? (Not that I want to gross you out, but every day millions of dogs lift their legs in a fond salute to their favorite sprinkler head!) These things can and WILL come back up your irrigation pipes and into your drinking water if you don't stop them. If you have a well they can go down your well and into everyone else's drinking water. If you are on a community water system they could go back up into the pipes and poison your neighbors. The valves that turn on and off your irrigation system are not sufficient to stop backflow. The purpose of the backflow preventer is to protect you when the valve breaks or leaks, which all valves will do eventually. Saving a little money by skipping the backflow preventer will not seem so smart after you spend a small fortune on hospital bills (or funeral expenses) for a poisoned family member or pet!
Now wait a minute, some people say, doesn't the water pressure in the system keep the irrigation water from going backwards? Yes, most of the time it does. But there are times when the water pressure drops in the supply system, and this is when the backflow occurs. No, it is not a frequent occurrence. But it does happen more often than you think. Such as when they have to shut off the water to repair a water pipe, or hook up a new pipe. This makes construction projects easily the most common cause of backflow problems. Fire fighting is another common cause of backflow. Fire trucks use huge pumps to suck the water out of the fire hydrants. This often causes the water pressure in the water system to drop, and backflow will occur in the surrounding neighborhoods. You can do a quick experiment yourself and create backflow. Simply tun off the water valve leading to your house. Next have someone turn on a faucet. Now turn on a different faucet that is higher than the first. You will hear air being sucked into the higher faucet. You just created backflow in your house piping. Pretty easy, wasn't it?
Another common argument against the need for backflow preventers is that if all the valves are closed the water can't go backwards through them. So the valves will prevent backflow. The obvious problem with this is that if the backflow occurs at a time when the valve is open, the valve will not stop backflow! But even when the valve is closed it may not prevent backflow. A standard manually operated valve will stop backflow when it is closed-- if the valve if fully closed, has good seals, and does not leak. However most of the automatic valves, such as the electric solenoid valves used for irrigation systems, will not stop backflow even when fully closed. This is because these valves are directional in design, if you look on the valve you sill see that it has an arrow on it showing the flow direction. If the flow is reversed, the valve will not completely close and will leak (that's why the valve has the arrow on it to warn you not to install it backwards.) Thus when backflow occurs and the flow direction reverses, an automatic valve will not stop the backward flow.


The following information was from Jess Stryker's Irrigation Tutorials, someone that we have listed as one of our resources that is benefiting the industry.