Abstract

Outdoor water use represents a significant portion of residential water consumption, particularly in regions experiencing rising water costs and increasing drought pressures. Thoughtful landscape design and efficient irrigation strategies can dramatically reduce water use without compromising aesthetics or functionality. EPA’s WaterSense Outdoor Water Budget Tool Version 2.0 provides a data-driven framework for evaluating and designing water-efficient landscapes by comparing a proposed design against a standardized baseline. This article explains the evolution of the WaterSense program, the structure and assumptions of the updated tool, and practical applications for builders, designers, sustainability professionals, and property owners seeking measurable reductions in outdoor water consumption.

The Growing Importance of Outdoor Water Efficiency

Water bills are rising, and drought conditions are increasingly common across the United States. In many communities, outdoor irrigation is one of the largest contributors to residential water demand, especially during peak summer months. In some cases, water scarcity has led to voluntary or mandatory restrictions on outdoor watering.

At the same time, reducing water use provides clear financial and environmental benefits. Lower water consumption reduces utility costs, supports long-term water resource resilience, and helps projects achieve certification under green building standards such as LEED for Homes and other performance-based rating systems.

Outdoor water use, however, is often less scrutinized than indoor fixtures and appliances. Toilets, faucets, and showers are commonly upgraded to WaterSense-labeled models, yet landscapes are frequently designed with default assumptions: expansive cool-season turf irrigated by spray systems. These decisions can lock in high water demand for decades.

To address this, EPA’s WaterSense program developed the Outdoor Water Budget Tool to quantify and compare landscape water use. Version 2.0 represents a significant refinement of that tool, expanding its functionality, updating assumptions, and improving usability for a broader audience.

Evolution of the WaterSense Homes Program

The WaterSense Specification for Homes was first released in 2009 as the nation’s first national certification focused exclusively on residential water efficiency. Version 1 of the specification included numerous prescriptive requirements covering both indoor and outdoor water use. One of those requirements was the use of the WaterSense Outdoor Water Budget Tool for landscape design.

In 2022, Version 2 of the specification became effective. Rather than relying heavily on prescriptive requirements, the revised framework emphasizes performance. Homes must demonstrate at least 30% greater water efficiency than a typical new home. Builders work through approved Home Certification Organizations (HCOs), which each have EPA-reviewed methods for verifying compliance with the 30% target.

Under Version 2, there are only two mandatory requirements:

• Installation of WaterSense-labeled plumbing fixtures
• Verification that the home is free of leaks

All other water reductions—indoor and outdoor—are evaluated through the HCO’s certification method.

Importantly, the Outdoor Water Budget Tool is no longer mandatory under the WaterSense Homes specification. However, reductions in outdoor water use remain essential to achieving the 30% efficiency target. It is extremely difficult to reach that threshold through indoor reductions alone. As a result, the tool remains a valuable design and verification resource.

Version 2.0 of the Water Budget Tool was released to reflect this shift: it is no longer a pass/fail compliance instrument but a flexible design and evaluation tool that supports multiple certification pathways and practical applications.

Core Concept: Baseline vs. Designed Landscape

At its foundation, the WaterSense Outdoor Water Budget Tool compares two scenarios:

1. Baseline Landscape
   Assumes a landscape entirely composed of cool-season turf grass irrigated with spray irrigation. This represents a water-intensive but common default scenario.
2. Designed Landscape
   Reflects the actual proposed or existing landscape design, including plant types, irrigation equipment, and system controls.

The tool calculates water use for both scenarios and determines the percent reduction achieved by the designed landscape relative to the baseline.

The baseline is intentionally conservative. Cool-season turf and spray irrigation represent high water demand and lower distribution uniformity. By comparing against this intensive scenario, designers can see clearly how plant selection and irrigation upgrades reduce consumption.

Key Enhancements in Version 2.0

Version 2.0 introduces several significant improvements.

Annual Water Use Calculation

Previous versions focused primarily on peak month demand. Version 2.0 expands analysis to estimate annual water use. This provides a more comprehensive understanding of total consumption over time and aligns more closely with utility billing cycles and performance certification systems.

Peak month results are still available, but annual totals are now central.

Zip Code–Specific Climate Data

The tool requires two critical inputs:

• Zip code
• Total landscape area

Climate data—including monthly rainfall and reference evapotranspiration (ET)—is automatically populated based on zip code. This ensures geographic specificity and reflects local environmental conditions.

Reference ET and rainfall data are drawn from national datasets processed to provide consistent coverage.

Growing Season Determination

A major refinement in Version 2.0 is the incorporation of a defined growing season by zip code.

Rather than assuming irrigation demand year-round, the tool uses temperature-based growing degree day calculations to determine when plants are actively growing and likely to require irrigation. Months outside the growing season are assigned zero irrigation need, even if ET exceeds rainfall. This adjustment significantly improves realism in colder climates.

Effective Rainfall Assumption

Not all rainfall contributes directly to plant water needs. The tool assumes that 25% of monthly rainfall is effectively available to the landscape. This conservative assumption reflects runoff and other losses.

Net ET (plant demand) is calculated as:

Monthly ET – Effective Rainfall

If rainfall exceeds ET, irrigation need is set to zero.

Irrigation Application Rate

One of the most important assumptions in Version 2.0 acknowledges real-world behavior. Research indicates that residential irrigation systems typically apply only about 58% of theoretical plant water demand.

Rather than assuming perfect irrigation matching plant demand, the baseline and design scenarios both apply a default irrigation application rate of 58%.

This assumption reflects observed behavior in the field and prevents overestimation of water use. However, the user may override this value if more accurate local data is available or if evaluating commercial systems, which may operate closer to 100% of plant demand.

Expanded Zone Capacity

Version 2.0 significantly increases the number of landscape zones that can be entered, making the tool applicable to larger residential, multifamily, or even commercial landscapes.

Credit for WaterSense-Labeled Technologies

The updated tool provides explicit water savings credit for:

• WaterSense-labeled weather-based irrigation controllers
• Soil moisture sensors
• Rain sensors
• Pressure-regulated spray sprinkler bodies
• Systems designed or audited by irrigation professionals certified under a WaterSense-labeled program

These savings are applied system-wide and reflect documented performance improvements.

Practical Design Application: A New Construction Example

Consider a hypothetical new build in South Jordan, Utah, with approximately 3,100 square feet of irrigable landscape area.

Local code requires:

• Drip irrigation (micro-irrigation) for non-turf areas
• Separate irrigation zones for turf and planting beds
• WaterSense-labeled irrigation controllers with rain delay
• Turf limited to no more than 35% of landscaped area

Entering the site’s zip code and total landscape area into the tool automatically populates monthly ET, rainfall, and growing season data.

A baseline scenario assuming full cool-season turf and spray irrigation produces an estimated annual outdoor water use.

The proposed design includes:

• 35% cool-season turf with spray irrigation
• Non-turf planting beds irrigated with micro-irrigation
• A non-irrigated patio area
• A WaterSense-labeled weather-based irrigation controller

The tool calculates monthly and annual water use for the design scenario and compares it to the baseline.

Without system-wide efficiency features, the design may fall slightly short of a 30% reduction. However, adding the WaterSense-labeled controller and rain sensor yields sufficient additional savings to surpass the 30% reduction target.

This demonstrates how thoughtful irrigation technology selection can close performance gaps even when turf remains part of the design.

Retrofit Application: A Landscape Redesign Scenario

The tool is equally valuable for existing homes considering landscape transformations.

Imagine a homeowner in Augusta, Georgia with 10,000 square feet of irrigated landscape. The current design is primarily turf, with limited planting beds.

The homeowner wants to:

• Add a large vegetable garden
• Increase curb appeal with additional planting beds
• Maintain green turf comparable to neighbors

The baseline landscape is entered. Because the homeowner irrigates aggressively, the irrigation application rate is adjusted upward from 58% to 80%.

The redesigned landscape includes:

• Warm-season turf (zoysia)
• Expanded planting beds
• A vegetable garden
• A rain sensor

The tool compares annual water use before and after redesign. Even though turf remains a large component, switching to warm-season grass and incorporating micro-irrigation for beds may reduce water demand relative to the original configuration.

This scenario illustrates how the tool can quantify trade-offs between aesthetics, recreation, and water efficiency.

Integration with Green Building Certification Systems

Although no longer required under the WaterSense Homes specification, the tool remains highly relevant to certification programs that evaluate outdoor water use under performance pathways.

Programs such as LEED for Homes and other HCO-administered rating systems require total water use calculations—including outdoor irrigation—when pursuing performance-based points.

Using the Water Budget Tool allows designers and builders to:

• Quantify outdoor water savings
• Support documentation for certification review
• Explore alternative landscape strategies
• Demonstrate compliance with local water budget requirements

In performance pathways, outdoor reductions often contribute significantly to achieving overall water reduction thresholds.

Broader Applications Beyond Certification

The WaterSense Outdoor Water Budget Tool Version 2.0 can serve multiple audiences:

• Builders designing new subdivisions
• Landscape architects optimizing plant selection
• Irrigation professionals evaluating retrofits
• Property managers assessing water use
• Municipalities establishing water budgets
• Utilities promoting conservation incentives

The tool can also provide rough comparisons between theoretical water use and actual metered data, offering insights into irrigation performance and potential inefficiencies.

While not designed as a billing reconciliation instrument, it can highlight discrepancies that warrant further investigation.

The Strategic Importance of Outdoor Water Management

Outdoor irrigation is highly visible. Lawns and landscapes shape community aesthetics, property values, and homeowner identity. Yet these choices have long-term resource implications.

Designing for water efficiency does not require eliminating landscape function. Rather, it involves:

• Selecting climate-appropriate plant species
• Separating irrigation zones
• Using efficient distribution methods
• Installing smart controllers
• Accounting for realistic irrigation behavior

Version 2.0 of the Water Budget Tool translates these design decisions into measurable outcomes.

By shifting from prescriptive rules to performance-based evaluation, the updated WaterSense framework empowers professionals to innovate while maintaining accountability to water reduction targets.

As climate pressures intensify and water costs continue rising, integrating tools like this into standard design practice will become increasingly essential.

Conclusion

EPA’s WaterSense Outdoor Water Budget Tool Version 2.0 represents a mature, data-driven approach to landscape water efficiency. It moves beyond rigid compliance toward flexible performance evaluation, incorporating climate-specific data, realistic irrigation assumptions, and system-wide efficiency credits.

For sustainability professionals, builders, and landscape designers, the tool offers a transparent framework for quantifying outdoor water use and identifying meaningful reduction strategies.

Water-efficient landscapes are no longer simply a best practice; they are central to resilient, cost-effective, and certifiable green building.

Green Home Institute continues to support education and professional development around tools like this to help advance healthier and more sustainable residential environments.

Key Takeaways

• The WaterSense Outdoor Water Budget Tool compares a water-intensive turf baseline to a proposed landscape design.
• Version 2.0 calculates annual water use, not just peak month demand.
• Climate data is automatically populated by zip code, including growing season determination.
• A default irrigation application rate of 58% reflects observed residential irrigation behavior.
• Users can override application rates for commercial or atypical scenarios.
• The tool provides credit for WaterSense-labeled controllers, sensors, and certified irrigation professionals.
• Outdoor water reductions are essential for achieving the 30% water efficiency target under WaterSense Homes Version 2.
• The tool is useful for new construction, retrofits, certification documentation, and municipal water budgeting.
• Efficient plant selection and irrigation design can significantly reduce outdoor water use without sacrificing landscape function.