Plumbing Info

Flush those lines

Flushing the water supply lines or disinfecting contaminated plumbing components is crucial after a backflow incident.

Plumbing and water supply technology is more advanced than ever, however backflow issues and line breaches can still happen. Additionally, there are many state and federal water-protection programs in place to ensure we are supplied with clean and safe drinking water. Even so, there is still a chance of getting contaminated water through your water supply.

Water suppliers are required to install backflow prevention devices at many areas to protect water from becoming contaminated due to cross connections. Water suppliers can also treat distribution lines with chlorine. Enough chlorine is used to achieve a specific “contact time” that ensures the pipes are not contaminated. Modern plumbing codes also go a long way to help create a system of fittings and fixtures that create a clean water supply system.

Common backflow conditions

With all the protections in place, there can still be instances of backflow. With education and training, we can inform users of the danger of backflow contamination; which helps create safer communities. Unfortunately, despite best efforts, we can all be affected by others tied into the same water delivery system.

A licensed plumber can install vacuum breakers on hose bibs, reduced pressure zone valves, double check valves and air gaps to protect the water supply system (municipal water system). While most of the users on the water system will follow best practices to avoid backflow, some people will still make decisions that create rick for contamination. Installing a booster pump without the proper check valve, filling a pool from any anti-syphon protection, or performing non-compliant plumbing repairs can all result in possible cross contamination.

Backflows and cross contamination can be caused by backpressure and back siphonage. Back siphonage could be caused by someone running over a fire hydrant. The high volume of water escaping through the broken hydrant can siphon water from the connected water system (for example the hose submerged in the pool water wile filling). The back siphonage could cause the pool water to be sucked into the water distribution system, potentially contaminating the water supply with unknown elements. Back pressure can be caused by a booster pump system when installed over the capacity of the incoming water supply.

If a residential user needs their water main repaired, it’s usually a straight forward operation. Shut the water off and remove all the mud and debris to expose the failed piping. Complete the repairs, restore water pressure, flush the lines and check for the correct static pressure. Back-fill, clean up, and the job is done.

Within this repair, our concern has been realized. What is the correct procedure to protect users from contamination? Is the simple flush of the lines enough? How much water should be used and how long does it take to flush the chemicals that may have entered from the ground soil?

The previous scenario is just one of many that are common to plumbing professionals. Every time the closed water supply system is accessed, there is potential for contamination.

Repairs and installations can cause contamination

Some companies only provide sewer and drain cleaning but do these providers have plumbing knowledge. Removing a stoppage is a typical procedure, but there can be other elements involve. For example, a water softener may need to be removed to access a clean-out. Depending on how this is handled, there could be a large increase in the chances of contamination.

After opening the clean-out, sewage could start escaping the drain system before the stoppage can be removed. If this sewage touches any part of the water softener, there is a huge risk for contamination. This includes water supply and waste removal lines to and from the softener. Without proper attention, this situation can happen to experienced professionals or the homeowner making their own repairs.

This is just one common scenario that can lead to water supply contamination. Although there are plumbing codes and backflow protections in place, there is still a possibility of potential contamination. We currently rely on a good flush after repairs to help ensure a safe and drinkable water supply. So after any plumbing repair job or project, flush, flush, flush those water delivery lines.


  1. Sam Li

    I love what you said about flushing water supply lines or disinfecting contaminated plumbing components and how it’s crucial after issues with a backflow device. Backflow seems to be a significant problem, so it’s a good idea to install a reliable backflow preventer. If I find myself in need, I’ll contact a reliable company to install such a device to give me some peace of mind.

  2. John

    Thanks for the informative article. Here in Canada, it important to make sure we set up in a way that we can blow out the backflow preventer if its located in a freezing climate. Alternatively, if you live in an area with lots of rainfall consider backfilling with free-draining materials like gravel to keep the device from becoming submerged. That makes testing and servicing easier and cleaner.


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