Guide to Backflow Prevention

Backflow can be complex and dangerous when it affects potable water systems. Preventing it is especially important to preserve public safety and protect large water supplies.

By adopting a few safe practices, you can keep backflow from becoming a problem in your plumbing system. Keep reading to learn what backflow is and how you can prevent it:

What Is Backflow and Why Should It Be Prevented?

The term backflow normally refers to a flow of water that has reversed towards its supply.

Backflow is usually undesirable in a plumbing system as it can lead to numerous health and safety risks. When water flows in the wrong direction, contaminants can follow it into the main water supply.

There are two primary forms of backflow that tend to occur:

  • Backsiphonage Backflow – Whenever the amount of pressure from the supply within a plumbing system drops lower than the rest of the system, backsiphonage can occur, drawing potentially contaminated water back towards the supply.
  • Backpressure Backflow – In the case of backpressure backflow, the plumbing, drainage or irrigation system builds up pressure over time, overtaking that of the supply. This pressure discrepancy leads to backflow in much the same way as backsiphonage, but the cause is essentially reversed.

How Backflow Happens

Backflow can occur at any time due either backsiphonage or backpressure. However, for backflow to become a problem, contaminants need to be involved, which can only occur under specific conditions.

Hazardous backflow occurs when there is a cross-connection that joins the general potable water system with another system that (unlike the potable water system) can potentially pull foreign substances into itself, drawing non-potable water into the potable system. When pressure at the supply side of the system ends up lower than that of the attached plumbing, water sucks back into it, taking whatever materials it was touching along for the ride.

Risks of Backflow

Backflow can pose serious health risks to those consuming contaminated water. However, the exact risks depend on the type of contaminants at play, which in turn depend entirely on the kinds of systems that are attached to the potable water supply.

Among the most common risky cross-connection systems are:

  • Irrigation – Both household and commercial irrigation systems have the potential to bring about serious imbalances in the potable water supply by pulling foreign substances and microorganisms into it whenever backflow occurs. Any irrigation system in direct contact with soil or placed at soil level can potentially do this if left unprotected.
  • Septic Drainage – Septic systems are normally designed to separate water that has come into contact with human (or animal) waste from clean, potable water by default as backflow involving such contaminants could cause serious illnesses.
  • Gray Water Runoff – Water poured into sinks, baths, etc. is also normally separated from the potable water supply to prevent hazardous backflow events from occurring.

Backflow Prevention

Backflow can be a serious issue if left unchecked.

Thankfully, there are multiple means of addressing backflow before it ever even occurs:

Backflow Prevention Techniques

Backflow prevention techniques or “control methods” keep water from moving from a connected system back into the potable water supply. Among the many control methods available, an air gap is the simplest.

Air gaps consist of a literal gap — they completely separate the potable water supply from wastewater in sinks, bathtubs and more by keeping the faucet or supply opening away from the flood area that collects used water.

Backflow Prevention Devices

Where air gaps and similar approaches may be impractical, a purpose-built backflow device, such as an atmospheric vacuum breaker, should be used. These accomplish the same effect via mechanical means. 

An atmospheric vacuum breaker leverages air and the lack thereof to manipulate an air-inlet poppet, which seals to prevent backflow in the case of supply-side pressure drops. Another device called a dual check can seal off the water supply under similar conditions, but features a dual backflow valve design that functions even if one valve stops working.Preventing backflow in potable water systems is critical to keeping people safe from unknown contaminants. To find out more about how Fluid Services can help, check out our backflow prevention services.

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