Backflow Prevention
What is a backflow prevention device and why do I need one?
Backflow preventing is probably the most important consideration when installing a new irrigation system. When you install a sprinkler system, the water must come from your potable water supply. This means that the new system is going to be connected to the city water supply somewhere. In Houston, like most large cities, the water purveyor charges us based on monthly water use. Therefore we have a water meter somewhere on our property (sometimes on the neighbors property). So the irrigation system ties into the water supply somewhere between the water meter and your house, see diagram below.
OK, so we have to tie into the water line, what does that have to do with backflow prevention, you might be asking. Well, all of these pipes are under pressure. That means that the water inside the pipes has the potential to move somewhere if given the chance. It may seem obvious that the water will flow from the higher pressure to lower pressure, like flowing from the pipes (higher pressure) to lower pressure (say your sink or bathtub). Most of the time the city water supply is the higher pressure so water will mostly flow from the city pipe to the house. However, there are circumstances where the pressure could be higher on your side of the water meter. If this happens, water will flow from your house to the city water supply. This is one case, called back pressure, when you need to protect the water supply from your water. When you have a sprinkler system attached and this backflow happens, there are all kinds of contaminates, like fertilizer, herbicides, pesticides and pet waste that could potentially get into the water supply.
There is one other type of backflow that could happen which is caused by siphoning. This happens when there is a sudden drop in the city water pressure such as a fire truck opens a fire hydrant near your house. This also could cause water to flow backwards through your water meter.
I think we have established that it is possible for water to flow from your property to the city water system. If this happens and the drinking water in your pipe flows backwards, it is not that critical. However, you don't want the water from your irrigation system to do the same. Therefore, it is extremely important to put a device in-line that will prevent this backflow. Hence the name backflow prevention.
In the State of Texas, there are only 5 types of backflow devices that are allowed. The first is called an air gap. This is what you have in your sinks, bath tub, and toilets. There is a gap between the pressurized pipes and the contaminated water. The other four are all used in irrigation systems. They are called RPZ (Reduced Pressure Zone), APB (Atmospheric Vacuum Breaker), DCVA (Double Check Valve Assembly) and PVB (Pressure Vacuum Breaker). If you want to learn more about these devices in great technical detail I recommend a few good websites like www.backflow.com and American Backflow Prevention Association, but if you just want an great overview of how these devices work and a brief history of backflow prevention, I highly recommend Febco's Cross Connection Control Handbook. They are one of the leading manufactures of backflow devices. This is a 12 page PDF file that is easy to read and very thorough. We have included this to download for your convenience, click here to download. All four of these have different requirements for installation. For those of you who are wondering, the RPZ is the top of the line backflow prevention devices and can be used for just about any residential irrigation system in Texas.
As a homeowner, you are partially responsible for protecting the water supply. You are actually liable for contamination that is derived from your property. Therefore, it is extremely important that you use the appropriate professionals to make the connection for your sprinkler system. In the state of Texas that means a plumber or licensed irrigator. There are many people out there that are putting in sprinkler systems that are not licensed and they are putting there customers (and the rest of the community on the water supply) at risk. Don't make the mistake of using someone that is not licensed to make this connection. Also, make sure that your irrigation professional pulls the appropriate permits if they are going to make a cross connection to the water supply.
The last thing to cover for the homeowner, is certification. As mentioned above, make sure that your contractor pulls a permit, gets a backflow certification (testing by a state licensed backflow certifier) AND gets the city to give the backflow prevention device a final inspection. Make sure that ALL of these are going to be done by your irrigator.
If you have any questions about backflow prevention, give us a call and we will be glad to answer any questions you may have.