Denver CO (Aug. 14, 2026) — The Colorado Plumbing Board has unanimously approved adoption of IAPMO’s Uniform Plumbing Code^® (UPC^®) Appendix M — the Water Demand Calculator^® — into Chapter 6 of the state’s adopted International Plumbing Code as an alternative methodology for sizing water supply piping in single- and multifamily buildings. It is now available for voluntary statewide use.

Appendix M's modern, science-based approach to sizing water supply piping gives designers and builders a new option for improving plumbing system performance, water efficiency and public health.

“IAPMO commends the Colorado Plumbing Board for adopting a modern, science-based approach to pipe sizing,” said Christina Kaeini, IAPMO senior director of Government Relations. “The Water Demand Calculator reflects today’s water use patterns and can help lower costs, improve efficiency, and enhance water quality. We appreciate the board’s leadership and the support of stakeholders and industry partners.”

Unlike traditional pipe-sizing methods based largely on decades-old assumptions about water use, the Water Demand Calculator uses statistical analysis to more accurately predict peak demand based on modern plumbing fixtures and actual patterns of water use.

Properly sizing water supply piping can reduce construction costs and water and water-heating energy consumption while improving hot-water delivery and reducing water stagnation. By minimizing unnecessary volumes of water sitting in premise plumbing systems, right-sizing can also help reduce conditions that may contribute to bacterial growth, including Legionella.

The Water Demand Calculator represents the result of a multiyear research effort to develop a statistically based methodology for sizing water supply piping. By more accurately matching pipe capacity to expected demand, the tool addresses concerns associated with oversized plumbing systems while supporting more efficient use of water and energy.

The Colorado Plumbing Board establishes minimum statewide building standards. Local jurisdictions may adopt more stringent requirements but may not adopt standards less stringent than those recognized by the board.

Colorado is now the 12th state to adopt Appendix M into its codes and standards, joining California, Hawaii, Montana, Nevada, New Jersey, New Mexico, North Dakota, Oklahoma, Oregon, Washington and Wisconsin. The Water Demand Calculator has also been adopted by major cities including Houston, San Jose, Seattle and Vancouver, British Columbia.

Learn more about the Water Demand Calculator at iapmo.org/we-stand/water-demand-calculator.

About IAPMO

Now celebrating its centennial, the International Association of Plumbing and Mechanical Officials (IAPMO) is a global team of experts engaging industry and government for a safer built environment. Based in Ontario, California, IAPMO offers codes and standards, including the Uniform Plumbing Code, the Uniform Mechanical Code, as well as the UPC and UMC Certification Marks that serve as a consistent model for building professionals, manufacturers and researchers. The group's deep expertise in codes and standards is applied to its rigorous product testing, certification and inspection services, professional development offerings, policy and advocacy work. For more, visit iapmo.org.