RESNET’s Water Efficiency Rating System HERSH20®

What is HERSH20

Water resources are becoming increasingly strained in many parts of the country and water prices are increasing faster than energy prices. Water price increases are not based solely on availability of water, but also are significantly impacted by the costs to upgrade aging water infrastructure and water utility rate structures. This means that  the potential for water cost savings through water efficiency measures is available in nearly all regions of the U.S.

To address this issue RESNET has created a water efficiency rating system, HERSH2O

HERSH2O builds off of RESNET’s nationally recognized Home Energy Rating System (HERS®) Index, which is the gold standard for rating the energy efficiency of a home. HERSH2O is a system for rating whole-house water efficiency that includes both indoor and outdoor uses. With the average family spending more than $1,000 annually on water costs, HERSH2O provides a simple, easy to compare rating on a scale from 0-100+; where lower numbers mean less water use. The HERSH2O Index was developed as part of a partnership between RESNET and the International Code Council (ICC), Natural Resource Defense Council and the EPA WaterSense Program .

The basis for HERSH2O is the ANSI RESNET/ICC Standard 850. It is anticipated that this standard will be finalized by the end of 2019. The standard can be viewed here.

How is a HERSH2O Rating determined? What is the Home Being Rated Against?

A HERSH2O rating is determined by comparing the home that is being rated with a “Reference Home” that is representative of construction practices (plumbing products and practices) circa 2006. There were a number of data sources used to develop the models that provide an estimate for both indoor and outdoor water usage. These data sources include:

  • Residential End Uses of Water Study, 1 and 2
  • 2005 Residential Energy Consumption Survey
  • ANSI/RESNET/ICC 301-2014, Addendum A
  • DOE Technical Support Documents from 2006 NAECA Standards
  • World Water and Climate Atlas

What Went into the Development of HERSH2O?

HERSH2O underwent a consensus development process with input from more than 75 organizations. The Technical Guidelines Working group was responsible for drafting the guidelines, but there were five other subcommittees that contributed to its development, including:

1) Reference and Modelling

2) Indoor Water Use

3) Outdoor Water Use

4) Rating and Inspection Procedures

5) Rater Training

Following the approval of the Technical Guidelines by the RESNET Board, the standard development process began. Standard Development Committee 1100 is responsible for the development and maintenance of Standard 1101, a candidate-ANSI standard.

How to become a HERSH20 Rater?


Become a HERSH2O Rater

All active certified RESNET Home Energy Raters and Rating Field Inspectors are eligible to conduct HERSH2O ratings and/or field inspections after completing the online HERSH2O Rater Training program and meeting the criteria in the Implementation Guidelines for HERSH2O National Rollout 2020.

Become a HERSH2O Provider

All current RESNET accredited Rating Quality Assurance Providers (QA Provider) are eligible to become HERSH2O Rating Providers after meeting the following criteria in the Implementation Guidelines for HERSH2O National Rollout 2020 and completing the HERSH2O Provider Application.

How to become a CalCERTS/RESNET HERSH20 Rater?


RESNET/ICC Standard 850-2020 Technical Guidelines

Implementation Guidelines for HERSH2O 2020 National Rollout

RESNET Inspection and Verification Guidance for HERSH2O

HERSH2O Inspection Checklist

ICC Sustainability Membership Council Video Feature on HERSH2O

RESTalk Podcast on Introducing the RESNET Water Efficiency Rating System HERSH2O with Mark Johnson (ICC) and Jacob Atalla (KB Home)

Introducing RESNET HERSH20: RESNET’s Whole House Water Efficiency Rating Infographic