ANSI/RESNET/ICC 850-2025 Standard Calculation and Labeling of the Water Use Performance of Dwelling and Sleeping Units Using a Water Rating Index

This standard establishes a consistent, uniform methodology for evaluating, quantifying, and labeling the water use performance of one- and two-family dwellings. Using a comparative framework, the standard assesses the water use performance of an actual home against a reference home of identical geometry. The result is a standardized Water Rating Index (WRI), providing a clear, relative measure of water efficiency. A WRI score of 100 indicates that the rated home’s water use performance matches that of the reference home.

Designed to support water efficiency programs, code compliance pathways, rating systems and sustainability initiatives, this standard offers a reliable and technically robust approach to assessing residential water use performance.

This book includes:

• A uniform methodology for evaluating residential water use performance
• Procedures for quantifying water efficiency in one- and two-family dwellings
• Definition and calculation of the Water Rating Index (WRI)
• Requirements for comparing a rated home to a reference home of equal geometry
• Guidance for generating consistent, label-ready WRI scores
• Applications for codes, efficiency programs and sustainability certifications
• Documentation requirements that support repeatable and transparent ratings