Backflow occurs when water reverses course and begins to flow in the wrong direction. Serious contamination can result, leading to illnesses and even fatalities. For this reason, it’s important to test for backflow and address any problems immediately.

Backflow occurs when the water pressure in the water distribution system is lower than the water pressure in an individual system. There are two main causes of backflow: Backsiphonage & Backpressure.

Backsiphonage occurs when a negative or reduced pressure is applied at a building’s tap, creating the potential for contaminants to be siphoned into the drinking water system. Potential causes of backsiphonage include heavy water usage on a system, water main breaks, and unauthorized fire hydrant use.

Backpressure incidents can occur when the pressure on an individual system exceeds the pressure in the distribution system, resulting in undesirable gasses or liquids being introduced into the drinking water supply. Potential causes of backpressure include pumps, elevated piping, and thermal expansion.

Backflow into a public water system can pollute or contaminate the water in that system (i.e., backflow into a public water system can make the water in that system unusable or unsafe to drink), and each water supplier has a responsibility to provide water that is usable and safe to drink under all foreseeable circumstances. Furthermore, consumers generally have absolute faith that water delivered to them through a public water system is always safe to drink. For these reasons, each water supplier must take reasonable precautions to protect its public water system against backflow.

Mechanical backflow preventers have internal seals, springs, and moving parts that are subject to fouling, wear, or fatigue. Also, mechanical backflow preventers and air gaps can be bypassed. Therefore, all backflow preventers have to be tested periodically to ensure that they are functioning properly. A visual check of air gaps is sufficient, but mechanical backflow preventers have to be tested with properly calibrated gauge equipment.

With any backflow incident there is a risk of non-potable materials — those not intended for human consumption — flowing back into the local water system. This could include wastewater, industrial fluids, chemicals, fire sprinklers, or lawn irrigation water.

Backflow incidents can be avoided through the installation of a backflow prevention assembly. A backflow prevention assembly essentially turns pipe into a one-way street; water can flow in the intended direction but cannot flow backwards even in the presence of backflow or backsiphonage.

In order to ensure that these important devices are functioning properly, backflow assemblies should be tested on a yearly basis to confirm that the water distribution system is being adequately protected from potentially-harmful pollutants or contaminants.