What is Backflow?
In order to appreciate the need for backflow control measures, it is important to consider how our water distribution system functions. Our system is designed to operate under pressure provided by water stored in our elevated tank. The earthbound pull of gravity, aided by occasional contributions from our pumping stations, translates to a stable pressure forcing water through the underground mains seeking areas of reduced pressure.
Reduced pressure is created in water mains whenever customers draw water through their service connections. Opening a tap relieves the pressure in the main and water spills out of a customer's faucet. Prompted by constant pressure, water inside the mains rushes to fill the void created by the water escaping through the faucet. This scenario is imperceptibly repeated countless times throughout the Village each day resulting in an efficient water distribution system capable of satisfying all of our domestic, commercial, and fire protection water needs.
Unfortunately, our control over the pressurized environment is not absolute. Main breaks and fire fighting operations are two examples of activities capable of creating dramatic low pressure zones within our mains. During these types of events, the hydraulic gradient may shift enough to reverse the intended flow of water and actually draw water out of nearby service connections. If these connections are affixed to chemical mixing facilities or any non-potable water supply, the possibility exists that dangerous backflow can occur resulting in contamination of our public water supply.
Backflow, for our purposes, can essentially be considered a phenomenon derived from one or both of two possible sources: a backsiphonage situation or a backpressure situation. Backsiphonage is caused by reduced or negative pressure in supply piping. The main break and fire fighting scenarios described in the previous paragraph are prime examples of environments conducive to backsiphonage. A break in our underground pipes or a fire engine hooking up to a hydrant can create reduced or negative pressure zones that may draw water from sources beyond the sanitary control of the Village via service connections or cross connections attached to services.
Backpressure is backflow that can occur when our supply piping is connected to a non-potable system operating under higher pressure. For example, when fire sprinkling systems are charged for testing, or when our system supplies certain industrial processes that are utilizing water as a mixing or cleaning agent, it is possible to encounter higher pressures.