When we deliver clean, safe potable water from the water distribution system to a service line supplying a consumer facility, is our job of protecting the water supply finished? How about after the water flows into the water meter and then enters the building — has the danger to the building water quality been eliminated? While backflow prevention may have been installed at the service connection as containment or point-of-service protection, this will not protect the water quality within the customer’s system. We need to ensure water quality and safety for each and every fixture or appliance. We need to protect the water to the last free-flowing tap in the system.
Let’s talk about dead legs in water systems and the effect they can have on water quality and water safety. Neither the 2024 National Standard Plumbing Code (NSPC) nor the 2024 International Plumbing Code (IPC) explicitly mention dead legs. In Section 206, the 2024 Uniform Plumbing Code (UPC®) defines dead leg as “A section of potable water pipe which contains water that has no flow or does not circulate.” The 2024 UPC, in Section 309.6 Dead Legs, states: “Dead legs shall have a method of flushing.” The problem for those people working in the field is: What exactly makes a section of piping a dead leg? How long does the piping need be to be considered a dead leg? Is it 10 pipe diameters? Is it 60 inches? The model code does not seem to address how to make that decision. Some states have attempted to give more guidance on what should be considered a dead leg. The state of Oregon gives the following guidance: “A dead leg is a section of potable water pipe which contains water that has no flow or does not circulate. If the section of pipe is greater than 1.5 times the diameter of the pipe served, it is considered a dead leg and would require a method of flushing.”
Its reason and analysis are as follows:
“The concept of dead legs in a plumbing system has been a topic of discussion globally. Dead legs cause a pipe to be isolated from the regular flow of water promoting the growth of dangerous bacteria such as legionella. Industry guidelines for design criteria and water system management are recommended by experts to control bacteria growth in potable water systems. Industry professionals are designing systems without dead legs in new buildings to help mitigate any potential bacteria growth. The structures that will likely need attention will be existing buildings.
In an existing system, where dead legs may exist or are created after a fixture has been removed, the best solution is to try and remove the dead leg completely, all the way back to and including the connection. However, where a dead leg exists, a means of flushing or fluctuating the water within an isolated pipe is required, as it will prevent the water from becoming stagnant and contaminated.
The Oregon Plumbing Specialty Code does not specify a maximum length for a section of pipe to be considered a dead leg; therefore, a common length should be established for consistent installation and enforcement. 1.5 times the diameter of the pipe served is a common industry calculation that is used broadly across pharmaceutical and engineering practices.”
What Oregon has done makes sense. People may consider the 1.5 diameter length as too restrictive, but in truth, any length is an issue. The state of Illinois, in its administrative code, prohibits unused sections of water service or water distribution piping where water could become stagnant. Any developed length of more than 2 feet is considered a dead end and must be avoided. When I was working in the field, I saw many large facilities with dead legs that stretched at times to 100 feet or more in length. As changes were made to the facilities, the existing piping was allowed to remain even if it no longer served any fixtures or appliances. Rooms were repurposed and fixtures were removed, but the water piping that supplied those fixtures was capped and left in place. Dead legs are far too common in older industrial and institutional facilities.
The United States Centers for Disease Control and Prevention (CDC) also recommends that facilities eliminate sections of no- or low-water flow called dead legs. If they are not eliminated, CDC recommends the following: Flush low-flow piping runs and dead legs at least weekly and flush infrequently used fixtures (e.g., eyewash stations, emergency showers) regularly as needed to maintain water quality parameters within control limits. Eliminating dead legs is clearly the right direction to move in. The flushing of dead legs adds a maintenance requirement to what may be an already overburdened staff. It becomes another thing that can fall through the cracks and endanger our water supply.
No-flow systems do exist in modern buildings — a building’s standpipe system or its water-based fire protection systems are perfect examples of that. In these cases, we install the proper backflow protection to ensure the stagnant water will not affect the potable water systems. We then test and maintain that protection on a regular basis to safeguard our systems. Dead legs should be pointed out to the end user when cross-connection surveys are performed. The removal of this piping should be included with the facility recommendations. Protecting our water is a never-ending task and we must continue to be proactive in our approach.
Audrey Hepburn, one of my favorite actresses, considered being a UNICEF Goodwill Ambassador as the greatest role of her career. She said, “Water is life, and clean water means health.” Protecting water is what we do in our industry; the plumber protects the health of the world.
