IAPMO is pleased to announce the publication of 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 (ASPE), Water Quality Research Foundation (WQRF), and the University of Cincinnati, the Water Demand Calculator’s methodology has been incorporated into the Uniform Plumbing Code (UPC), the Water Efficiency and Sanitation Standard (WE•Stand), 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 and provides a valuable resource for designers and regulators seeking a modern approach to residential water supply sizing. The standards can be obtained at  https://iapmostore.org/search.php?search_query=z1403

“Publication of IAPMO Z1403 marks an important milestone in the plumbing industry's transition to data-driven water system design,” said Terry Burger, IAPMO senior director of standards development. “The standard provides a practical tool for right-sizing plumbing systems, helping to reduce unnecessary construction costs, improve energy efficiency, and address water quality concerns associated with oversized piping systems.”

The standard was developed through IAPMO's ANSI- and SCC-accredited consensus processes with participation from a broad cross-section of stakeholders, including plumbing engineers, code officials, manufacturers, contractors, utilities, educators, and public interest representatives. The resulting document establishes a consistent methodology that can be adopted and referenced.