Water Demand Calculator published as a stand-alone document

ONTARIO, CA — The International Association of Plumbing and Mechanical Officials (IAPMO®) published IAPMO/UPC/Appendix M-2021, Peak Water Demand Calculator, as a stand-alone document. This document is a direct extract from Annex M of the 2021 report Uniform Plumbing Code (UPC®),which was developed through an ANSI accredited development process. All references to other sections of the UPC were also extracted to avoid dependency on additional documents. The IAPMO/UPC/Appendix M-2021 is a document that can be easily used and adopted by any jurisdiction for water and energy conservation, to improve housing affordability, and to improve the water quality.

A copy of IAPMO/UPC/Appendix M-2021 can be purchased here:


Respond to Deep Concerns

The water demand calculatorMT (WDC) is the first significant update for sizing water pipes in buildings since the development of Hunter’s Curve over 80 years ago. It is the result of a multi-year effort led by IAPMO to develop a new method of pipe sizing based on statistics, resulting from a need to solve the problems of water safety and water waste and energy due to oversized water supply lines in homes and buildings. Plumbing systems in new home construction are routinely overbuilt, increasing housing costs because the most commonly used pipe sizing formula is nearly 90 years old; developed long before the advent of today’s innovative low output fixtures and appliances.

The WDC provides a method for estimating the demand load for the building’s water supply and major branches for single-family and multi-family dwellings with plumbing fixtures, fixture fittings, and water-efficient fixtures. It provides examples for determining flow rate, which can then be used to size plumbing supply piping. The IAPMO WDC accurately predicts peak water demand in single-family homes and apartment buildings, reducing the structure’s carbon footprint and saving consumers on home heating energy bills. water and water for the life of the plumbing system.

Significant savings

Builders who use this document for residential projects can realize significant cost savings from its improved methods for determining proper pipe sizing, according to a study by a third-party engineering firm. Results from both studies show that the total average savings for a typical 2,379 square foot single-family home in a high-cost labor market can exceed $2,000 and as high as $5,000, depending on location. For multi-family apartment buildings, the potential savings are even higher and can exceed $100,000 on a 45-unit multi-family building, especially when meter connection fees are high due to water scarcity. Both studies are available at https://www.uniformcodes.org/water-demand-calculator/.

The WDC is a powerful and indispensable tool for bringing pipe sizing methodology into the 21st century. The primary benefits of applying WDC relate to addressing water quality issues associated with aging water in oversized plumbing systems and water and energy efficiency. However, WDC also significantly reduces construction costs and increases homeowner satisfaction when using modern and efficient plumbing products, which also makes the application of WDC attractive to builders.

For questions about the WDC, please contact Dan Cole at 708/995-3009 or [email protected]

Eleanor C. William