What Is Water Backflow?

In any plumbing system, there are two streams of water that must be separated at all times. One is the flow of the fresh supply of water, which may be potable or non-potable water.

This is the main supply of water that reaches all the faucets and fixtures of your house, such as water heaters and flush tanks.

The other stream of water is the wastewater that must flow out of your house and into the sewage line.

This is the water that flows from kitchen and shower drains as well as toilets and is directed outside into the municipal sewage tank.

The mixing of water from these two streams can be messy and inconvenient and extremely dangerous. Contamination of the main supply, especially lines of potable water, can cause a variety of diseases.

The wastewater can contain many germs, bacteria and harmful chemicals that can be severely hazardous to your health.

Backflow refers to the flow of water in undesirable directions or the cross-connection of these two streams of water.

What Causes a Backflow?

Three main reasons can cause backflows.

Back Pressure

Back pressure refers to the sudden increase in pressure of the water flowing in the waste line.

When the pressure of the wastewater stream is more than the main water supply, the water from the waste line rushes back through the system and contaminates the water supply.

This can be caused by water heaters which are do not have adequate vents. The heat released by the water heater into the plumbing system leads to an increase in pressure that causes backflow.

Back Siphonage

Back siphonage refers to the creation of a vacuum or negative pressure in the water line, which pushes the wastewater to gush up and fill up the space. The negative pressure is caused by a disruption in the main water supply.

The disruption can be caused by excess use of water, construction activities or fire fighting activities. Back siphonage often occurs in toilets and sinks.

Sewer Pipe Damage

The wastewater from any plumbing system is carried out of the house to the sewage system through sewerage pipes. These pipes can break down or get damaged over time, which can lead to the backflow of contaminated sewage water.

Signs of backflow caused by sewer pipe damage are foul smells and dirty water coming from plumbing fixtures in your home.

How to Prevent Water Backflow

Once water backflow occurs, its negative consequences can be very difficult to undo. Hence, prevention is critical. There are two main ways to prevent water backflow.

Air Gaps

An air gap is essentially an unobstructed space that is created between the main water supply and the wastewater line in order to prevent backflow. This is a simple way to prevent backflow that is today used in most plumbing systems.

An air gap is twice the diameter of the water supply pipe and is usually placed at the end of the supply to create positive air pressure in order to prevent backflow.

Backflow Prevention Devices

There are a number of plumbing devices that can help you prevent backflow. For instance, many plumbing systems have valves that are mechanically triggered by the backflow of water to stop the flow of water.

There can be various configurations of using multiple valves in order to prevent the backflow of water. For instance, a pressure vacuum breaker assembly system is used to avoid backflow that occurs through back-siphonage.

A pressure vacuum breaker assembly system employs a check valve operated by a spring and a dual shutoff valve.

A reduced pressure backflow prevention assembly can be used for backflow that occurs due to either back siphonage or back pressure.

Bottom Line

Water backflow is a severe plumbing issue that needs to be prevented to avoid contamination of the water supply. Backflow refers to the flow of water in the plumbing system in undesirable directions.

Contamination of water supply can be a serious health hazard. Backflow can be caused by three main reasons, back pressure, back siphonage and sewer pipe damage.

Back pressure is caused by excessive force in the wastewater line, whereas back siphonage is caused by negative pressure in the main water supply. Sewer pipe damage occurs due to wear and tear over time.

Backflow of water can be prevented in two main ways. Air gaps are a physical separation between the two water lines that ensures the regulation of pressure. Other than that, various assemblies of valves can be installed as backflow prevention devices.

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