California Approves Water Demand Calculator® as Alternate Standard for Estimating Peak Water Demand

The California Building Standards Commission has approved the adoption of IAPMO’s Uniform Plumbing Code (UPC®) Appendix M — the Water Demand Calculator® — into the California Plumbing Code (CPC) as an alternative methodology for estimating peak water demand that impacts water pipe sizing in single family dwellings and multifamily buildings. The alternative approach will be available for statewide use on a voluntary basis starting July 1, 2024.

Introduction to the Benefits of the Water Saving Tool

How to Use the Water Demand Calculator

How the ANSI-Accredited Process Was Used to Adopt the Water Demand Calculator 

Adoption of the Water Demand Calculator in California

Water Demand Calculator Sizing Applications

A revolutionary tool, the Water Demand Calculator more accurately estimates 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. At the same time, proper sizing greatly minimizes the potential threat of bacterial growth within the system, which can lead to such serious health risks as Legionnaire’s disease.

In 2021, the Statewide Utility Codes and Standards Team submitted a Title 24 Petition to adopt Appendix M into the CPC during the 2022 Intervening Code Adoption Cycle. The petition was accompanied by the letters of support from 20 organizations including the California Legislature, cities, water utilities, engineering firms, and the California Water Efficiency Partnership.

The Water Demand Calculator is the first major update impacting plumbing sizing since the 1940s. 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 joins states including Hawaii, Montana, Nevada, New Jersey, New Mexico, North Dakota, Oregon, Washington and Wisconsin, as well as the cities of Seattle, Washington and Vancouver, British Columbia, in adopting Appendix M into their codes and standards.

The Water Demand Calculator version 2.2 and user guide may be downloaded for free HERE.

Send me information on future live webinars

IAPMO Senior Director of Workforce Training and Development Randy Lorge led a webinar titled “How to Utilize the WDC to Size” on Feb. 21. To view the webinar, click here.

Click here for Water Demand Calculator courses Water Demand Calculator courses for CEU's supporting California adoption at