Backflow: Causes and Preventative Measures

When relying on a water company to provide you with clean water, most residents assume this is easy to achieve. But could you imagine finding out that you did not just have the usual flu that was running around, but had been poisoned by the very water you pay for? This would most likely be a case of backflow, which simply put is when water in an irrigation system, instead of flowing out, flows back in, carrying with it contamination from whatever was around the output source. This doesn’t have to be sewage; it could also be worms, debris, etc. Backflow devices keep instances like this from happening. When it comes to irrigation many toxins could be getting into the system; animal waste, pesticides, and fertilizer are all common examples of why backflow devices are required.


Major Offenders

The two major offenders of backflow are backsiphonage and backpressure. Backpressure materializes when a system’s pressure is superior to that of the city’s supply pressure. Typically occurring because of changes in piping elevation caused by pumps, or thermal expansion caused by a water heater, backpressure can be easily avoided by following a few simple steps.

A water heater’s thermal expansion is the most frequent cause of backpressure. The water heater is directly connected to the cold water line, and as we all know when something heats it also expands. If the pressure is even a small amount greater than the city’s supply pressure, you will have backpressure.

Backsiphonage is caused by a below average atmospheric pressure inside of a water system. Simply put, backflow happens when the pressure in a city’s water main becomes negative. Almost like the water supply is being sucked out of your house, backsiphonage is cause by high water withdrawal rates. One example of backsiphonage is if a construction crew is working and directly hits the city’s water main. The hose that is attached and submerged in toxic water at a local home will want to suck up any liquid causing the water to move to a lower pressure area, thus poisoning the city’s water.


Different Backflow Devices

Depending on the circumstances, installing a backflow device will require knowing whether the situation is considered a high-hazard or a low-hazard situation.

  • High-hazard– High-hazard means that any person consuming that fluid could be poisoned. Irrigation is always considered a high hazard because of the chemicals and wastes on the ground.
  • Low-hazard- Low-hazard would be a liquid that has a strange taste, color or smell. Low-hazard is drinkable but will not be pleasant to the senses.


Backflow devices have a tendency to be overlooked when installed; some customers will put them in without considering elevation, or even not reading the instructions properly and installing them backwards. Owner of Sprinkler Warehouse, Steve Okelberry suggested inquiring to the local AHJ before installing since they will have a recommendation as to where to place your backflow. Since the AHJ needs to inspect your backflow device annually, it is important that the AHJ have easy access. Having it placed ten feet off the ground because you need to compensate for elevation is not going to work when adjustments or repairs need to be made. The AHJ will inform you on which type of device to use for any project you might have, as well as where to place it. **Always check with the local authorities before installing any type of backflow device.**

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