Your Home Irrigation System and Backflow Device Working Together

Everyone knows that the Home Irrigation System is the sprinklers.
But are you aware of what a Backflow Device is? And do you know how these two work together?
According to Wikipedia definition a Backflow Device is used to protect potable water supplies from contamination or pollution due to backflow. In water supply systems, water is normally maintained at a significant pressure to enable water to flow from the tap, shower, or other fixture.
So basically... what flows in one direction cannot flow in the opposite direction.
Okay, now how do they work together? Why do you need to keep a Backflow Device on your sprinklers?
Dangerous and Deadly situations can occur and have occurred. 
One incident was reported in the October 31, 1997, issue of the Los Angeles Times, bringing to the nations attention that backflow incidents involving irrigation systems do happen. This article reported, "Drinking water in the system serving two schools and as many as 1,600 homes in Calabasas hillside neighborhoods was contaminated with treated sewage water intended for irrigation after a plumber working on a landscaping job mistakenly crossed two pipes." Several people became ill due to this cross connection and residents were warned not to drink from their faucets or from local water vending machines until the fresh water lines were flushed and tested. The plumber involved was exposed to potential litigation including the cost of the clean-up.
Now we are not talking about sprinkler systems that are a single sprinkler hooked up to a hose.
We are talking about Irrigation Systems with multiple in ground sprinklers.
These systems contain treatments and chemicals used on your grass/weeds that you do NOT want mixing with your drinking/bathing water.
That is how the Home Irrigation System and Backflow Device work together.
Your Backflow Device helps keep the water and chemicals used by your Home Irrigation System flowing downwards away from your home.