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WATER DEMAND CALCULATOR®
Estimating water supply demand for residential buildings
The WE-Stand and the Uniform Plumbing Code provides an alternative to Hunter’s Curve when estimating water supply demand for residential buildings including single- and multi-family dwellings. This Peak Water Demand Calculator estimates the supply demand for the whole building, as well as cold and hot water branches and risers for indoor water use based on today’s plumbing fixtures and appliances and usage patterns.
Provisions for using the Water Demand Calculator are published in the 2018, 2021 and 2024 UPC; and the 2020 and 2023 WE•Stand. These documents also contain a download link for the Water Demand Calculator.
System Requirements:
The Water Demand Calculator requires a compatible version of Excel 2009 or later to prevent loss of functionality as it uses active content (macros). For security reasons, the Microsoft Office has security features that disables the macros with a warning message. The message advises the user that active content has been detected. This does not mean that viruses have been detected. The source file comes from IAPMO, so the file can be trusted, and the macros can be enabled. Once the file is trusted, the warning will no longer appear. You may also need to check with your company's system's administrator for security permission to download a file with macros.
See below for instructions on how to enable the macros.
INSTRUCTIONS
To download the Water Demand Calculator, please submit your email address and select which version you need. You will receive an email with a download link.
Note: The download is a zip file that contains the calculator, you will need to unzip the file using any zip program before you can use it.
WATER DEMAND CALCULATOR
ENABLING MACROS AFTER DOWNLOADING WDC VERSION 2.2
1. Download the WDC v2.2 (Windows) or (Mac OS) above.
2. Open the downloaded file click enable editing 
3. Close the security risk warning
4. Unblock macros (modifying the file properties)
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SIGNIFICANT PROVISIONS (CURRENT EDITION)
Water Demand Calculator Task Group
IAPMO Seeks Water Demand Calculator Task Group Members. Interested in participating on the Water Demand Calculator Task Group? Read More
Disclaimer:
Although care has been taken to ensure the accuracy, completeness and reliability of the Water Demand Calculator (“Calculator”), neither IAPMO nor any other party makes any warranties, express or implied, or representations as to the accuracy of the Calculator. Neither IAPMO nor any other party assumes any liability or responsibility for any error or omissions in the information contained in or output by the Calculator. Neither IAPMO nor any other party assumes any responsibility for the consequences of use of such information, nor for any infringement of third party intellectual property rights which may result from its use.
Please email any comments on the calculator to Dan.Cole@IAPMO.org
WATER DEMAND CALCULATOR
SUCCESS STORIES
Water Demand Calculator Article Featured in The New York Times
In an article by Megy Karydes, the Water Demand Calculator is highlighted as a key solution to a critical issue: oversized plumbing pipes. These oversized pipes not only waste significant amounts of water but can also negatively impact water quality. Developed by IAPMO experts Dan Cole and Toju Omaghomi, the Water Demand Calculator helps ensure pipes are "right-sized" for optimal performance. As Christoph Lohr explains in the article, the Water Demand Calculator is a vital tool for creating more sustainable and efficient plumbing systems.
Castle Rock, Colorado, Adopts Water Demand Calculator® for Residential Water Supply Pipe Sizing
The Castle Rock, Colorado, town council has approved the adoption of IAPMO’s Uniform Plumbing Code (UPC®) Appendix M — the Water Demand Calculator® — as an alternative methodology for sizing water pipes in single- and multifamily buildings. The Castle Rock Town Code has been amended to require the use of the Water Demand Calculator for sizing water service lines and internal plumbing supply lines.
Villara Leads the Way as Early Adopter of IAPMO’s Water Demand Calculator
Appendix M of IAPMO’s Uniform Plumbing Code® (UPC®), otherwise known as the Water Demand Calculator®, will become part of the California Plumbing Code on July 1, providing an alternative methodology for estimating peak supply demand to enable right-sizing water pipes in single- and multifamily buildings
Seattle Advances Water Demand Calculator Use with Training
With an eye toward Seattle mandating use this year of IAPMO’s Uniform Plumbing Code (UPC®) Appendix M — the Water Demand Calculator® — for multifamily buildings, the county and local ASSE and IAPMO chapters recently held an in-person training for inspectors, installers and design professionals.
Vancouver Leads the Way on IAPMO’s Water Demand Calculator
Starting this spring, contractors and builders in the city of Vancouver, British Columbia, will have the option to use IAPMO’s Water Demand Calculator™ for potable water systems, a money-saving alternative to conventional pipe sizing that will also reduce the amount of stagnant water in pipes.
Wisconsin Approves Water Demand Calculator as Alternate Standard for Sizing Water Supply Piping
The Wisconsin Department of Safety and Professional Services has approved IAPMO’s Water Demand Calculator™ (WDC) as an alternate method for estimating the demand load for a building’s water supply and principle branches for one- and two-family dwellings in the state.