What is meant by a 'dead leg' in a cold water system, and why should it be avoided?

• A. A length of pipe with little to no water movement; can stagnate, harbor contaminants, and create dead zones; minimize by routing and using adequate valve placement.
• B. A type of drawing label.
• C. A device that filters sediment.
• D. A joint that expands under pressure.

Answer: (A)

A dead leg is a length of cold water pipe where water doesn’t flow regularly, so it sits stagnant or near-stagnant. When water isn’t moving, disinfectant residuals can drop, minerals and sediments can settle, and biofilms or contaminants can begin to build up. That can lead to poorer water quality, taste, and potential microbial growth in that unused section. It should be avoided by designing the system so outlets aren’t fed by long, unused runs—keep runs short, loop the piping back to ensure continuous flow, and use valves or strategically placed outlets to flush and maintain regular water movement. Regular use of fixtures also helps prevent stagnation.