Locate the water shutoff valve to your irrigation system and turn off the water. This shutoff valve should be located somewhere between your water supply and the backflow preventer; the shutoff valve may be located indoors in your basement, in a crawlspace, or outside underground in a valve box. TIP: Sometimes it is easiest to first locate where the water for your sprinkler system comes out of your house (where the backflow or valve boxes are on the exterior of your home) and then go to the corresponding location inside your home.
How do I tell the difference between my main water shut off and the sprinkler water shut off? The sprinkler water pipe often comes off of the main water pipe and then goes directly outside the house without splitting off. The house water pipe often splits off into multiple pipes.
What if I accidentally shut off the main water instead of the sprinkler water? To test this, simply test the water in your house (by turning on a sink). If you have no water to your house you can turn that valve back to the ‘ON” position and turn the other valve (the correct sprinkler water valve) to the ‘OFF’ position. Label this valve with a permanent marker or tag for future reference.
Once the water is shut off, if your home has an indoor drain (examples pictured) on or near the irrigation valve, you can release the remaining water by back draining the system. Simply go to your backflow device (examples pictured. Usually outdoors) and open the test ports with a flathead screwdriver. Bring a bucket or pitcher to the drain inside the house, open it and catch all water that comes out. Once finished draining, close the drain valve so air is not blown back into the home during the blowout.
After you have turned off your irrigation water supply, and if equipped; manually drained the system, you are ready to have your system “blown-out”, which involves using compressed air. This should be done by a licensed irrigation professional. While some homeowners might already own an air compressor, it is not recommended that homeowners blow-out the irrigation systems themselves; this is preferable not only as a general safety precaution but also to prevent other incidental damage(s) from occurring to the sprinkler system. Furthermore, while most consumer-owned air compressors can reach the required pressure or psi (pounds per square inch) to blow out an irrigation system, they do not generate the same volume of air in a given time (cubic feet per minute; cfm) to blow out the system as large, commercial compressors utilized by certified irrigation professionals. Air volume is as critical as air pressure. If an insufficient volume of air is used, after forcing some water out, the air will ride over the top of the water giving the appearance your system has been effectively blown out. This will result in the remaining water draining into low spots and subjecting the system to freeze damage.
Over the winter we turn the ball valves on the backflow preventer to a 45 degree angle relative to the pipe, and give the screws of the test-cocks a ¼ turn, where they are also at a 45-degree angle. This allows for any trapped water remaining in the valves to drain out to prevent any cracking due to freezing. This process will be reversed in the spring to start the system back up.