Posted July 2, 2024

IAPMO Hosts Water Demand Calculator Webinar as California Adopts Voluntary Use of Tool into California Plumbing Code

Calculator accurately predicts peak water demand in single-family homes and apartment buildings.

In accordance with the state of California making IAPMO’s Uniform Plumbing Code (UPC®) Appendix M — the Water Demand Calculator® — available for statewide use on a voluntary basis starting July 1,2024, IAPMO hosted a webinar that covers the benefits of using the tool to size plumbing in homes and apartment buildings.

Led by IAPMO Vice President of Technical Services and Research Christoph Lohr, P.E., the webinar provided guidance on using the revolutionary tool, which accurately predicts peak water demand in single-family homes and apartment buildings, reducing the carbon footprint of the structure and saving consumers on both their water and water heating-related energy utility bills for the entire life of the plumbing system. Proper sizing also greatly minimizes the potential threat of bacterial growth within the system, which can lead to such serious health risks as Legionnaires’ disease.

In 2021, the Statewide Utility Codes and Standards Team submitted a Title 24 Petition to adopt Appendix M into the California Plumbing Code during the 2022 Intervening Code Adoption Cycle. The California Water Efficiency Partnership (CalWEP) — a state chapter of the Alliance for Water Efficiency (AWE) of which IAPMO is a member — and 15 member agencies supported the petition.

The Water Demand Calculator reduces water aging, delivers hot water faster, generates significant construction cost savings, reduces the carbon footprint of the structure, and subsequently saves on water- and water heating-related utility bills for the entire life of the plumbing system. Instead of using flow rates and flush volumes from the 1940s, the Water Demand Calculator allows the user to “right-size” the cold and hot water distribution systems in homes and apartment buildings using modern information about flow rates and simultaneous use.

“Today marks an important moment in the history of the Water Demand Calculator as California, the fifth-largest economy in the world, officially implements the use of this 21st-century solution,” Lohr said. “The momentum in adoption of the Water Demand Calculator has been remarkable, with one-fifth of states and a host of other city and regional jurisdictions choosing to adopt this tool in a few short years. We are very grateful to all the volunteers and stakeholders who worked so hard to help make this day possible. IAPMO stands ready to help the California plumbing industry successfully understand how to utilize the Water Demand Calculator for its projects.”

The Water Demand Calculator represents the most impactful innovation in pipe sizing in nearly a century. It is the result of a multiyear effort to develop a new statistically based pipe-sizing method stemming from a need to address profound water safety and wasted water and energy concerns resulting from oversized water supply pipes in homes and buildings.

California is the 10th state to adopt Appendix M into its codes and standards, joining Hawaii, Montana, Nevada, New Jersey, New Mexico, North Dakota, Oregon, Washington and Wisconsin, as well as such major cities as Houston, San Jose, Seattle and Vancouver, British Columbia.

The Water Demand Calculator version 2.2 and user guide, as well as related videos, are available at