IAPMO Publishes 2026 Water Demand Calculator
IAPMO has published IAPMO/ANSI/CAN Z1403-2026, Water Demand Calculator, a new American National Standard and National Standard of Canada that provides a modern, statistically based method for estimating peak water demand in single-family and multifamily residential buildings.
The Water Demand Calculator was developed in response to the limitations of traditional water supply sizing methods based on assumptions dating back to the 1940s. By utilizing contemporary fixture flow rates, water-efficient appliance considerations and real-world usage patterns, the standard enables engineers, designers, contractors and authorities having jurisdiction to more accurately determine peak water demand and appropriately size water service lines, building supplies, mains, risers and branches.
Developed through a multi-year collaborative research effort involving IAPMO, American Society of Plumbing Engineers, Water Quality Research Foundation and the University of Cincinnati, the Water Demand Calculator’s methodology has been incorporated into the Uniform Plumbing Code, the Water Efficiency and Sanitation Standard and is adopted by numerous jurisdictions throughout the United States and Canada.
IAPMO/ANSI/CAN Z1403-2026 is available through the IAPMO Online Store in English and French. The standards can be obtained at https://iapmostore.org/search.php?search_query=z1403.
