The home construction industry is placing greater emphasis on outdoor water use, making irrigation system performance a larger part of the overall building design. To reflect updates to the 2025 ICC 700 National Green Building Standard (NGBS)®, the National Association of Home Builders (NAHB) has updated its Matrix of Water Efficiency Rating Systems, which leads to a Water Rating Index score (WRI), providing builders and contractors with a new framework for evaluating water efficiency before construction begins.
“These updated water efficiency requirements require that all indoor and outdoor water features, including irrigation systems, must be addressed as part of the project’s water performance plan,” said Amy Manz, program manager of sustainability and green building for NAHB.
For irrigation, this includes:
- Smart controllers that adjust watering schedules based on weather forecasts, soil moisture and plant needs.
- Rain sensors to automatically shut off irrigation during rainfall.
- Soil moisture sensors to prevent overwatering.
- Zoning to water different areas at different times or with different settings.
- Efficient nozzles and emitters to reduce runoff and evaporation.
- Integration with building management systems for real-time monitoring and control.
“The 2025 edition of the NGBS expands the WRI to apply to both new and existing buildings, allowing certification of total indoor and outdoor water use against a code-minimum baseline,” Manz said. “This means irrigation contractors can now contribute to reduced WRI scores for retrofits and renovations, not just new construction.”
Irrigation professionals don’t have to work exclusively on certified green homes to benefit from understanding the new framework. Familiarity with the standards can help irrigation contractors recommend more efficient system designs, discuss projected water use with builders and homeowners and better position themselves for projects where water efficiency is becoming a competitive differentiator.
What is the Water Rating Index?
The WRI measures a home’s projected indoor and outdoor water use compared with a code-minimum baseline. Outdoor water use, including irrigation and landscape watering, accounts for a significant portion of the overall score, Manz explained. The updated Matrix compares several leading water efficiency rating systems and provides builders, designers and contractors with a common language for discussing expected water use during the planning process.
“The Water Rating Index (WRI) is a recognized, above‑code water efficiency tool that can influence project outcomes, market positioning and long‑term performance and it allows an apples-to-apples comparison of water efficiency between systems,” Manz said. “Even if certification is not used, being able to compare systems before they are installed allows contractors and consumers to pick and choose the water efficiency components that will help them reach their goals most cost-effectively.”
Manz explained that the WRI assigns a score from 0 to 100, with lower scores indicating greater water efficiency. The matrix considers a home’s size, design and water saving features, including irrigation systems, rainwater or graywater reuse and other outdoor conservation measures.
“Many local governments and utilities are adopting water efficiency measures, such as tiered pricing or restrictions,” Manz said. “Understanding WRI helps contractors anticipate future compliance needs and position projects to meet upcoming local requirements before they are mandated.”
The impact of projecting property-wide water use
By estimating water demand, the WRI helps contractors evaluate irrigation designs, identify opportunities to reduce outdoor water use and demonstrate expected savings before installation. Builders use the information to support sustainability goals and communicate the value of efficient water management to prospective buyers.
Even without certification, being able to compare systems before installation allows contractors and consumers to pick and choose the water efficiency components that will help them reach their goals most cost-effectively.
“To achieve these enhanced irrigation efficiency measures, contractors are encouraged to take steps to plan early in the design phase, verify compliance, coordinate with landscape architects, document performance data diligently and train installers on maintenance needs,” Manz said.
As more municipalities adopt water efficiency requirements, modeling expected outdoor water use enables planning for water reuse and ensures compliance. It also helps planners and builders anticipate water demand under stressed scenarios, supporting more resilient, low‑water‑use design. Homeowners also benefit because they have a better understanding of water usage and estimated utility bills before purchasing a new home.
