Steps

Gather the site's peak watering month, reference evapotranspiration (ETo), and rainfall data using EPA's Water Budget Data Finder, entering the home's zip code.
In Part 1 of the Water Budget Tool (Baseline & LWA), input baseline landscape information to calculate the Landscape Water Allowance (LWA).
In Part 2 (LWR), input hydrozone, plant type, and irrigation-type data to calculate the Landscape Water Requirement (LWR), factoring in irrigation system efficiency since no system applies water at 100% efficiency.
Compare the LWR against the LWA in Part 3 (Results) of the tool to confirm the design falls within budget before finalizing plans.
Retain the completed Water Budget Tool output as part of the WaterSense New Homes inspection/verification documentation package.

Known gotchas

The tool's required ETo and rainfall inputs must come from EPA's own Water Budget Data Finder for the site's zip code — substituting a different weather-data source can produce a non-compliant or non-verifiable result.
Systems are intentionally scheduled to apply more water than the plants' theoretical need to offset real-world distribution inefficiency (wind drift, uneven coverage) — a naive 100%-efficiency calculation will understate the true water requirement.
This EPA tool computes a design-stage water budget for WaterSense New Homes certification; it is a different deliverable from a post-installation CLIA-style field audit, which measures actual as-built performance.

Design an irrigation system to comply with California's Model Water Efficient Landscape Ordinance (MWELO), including hydrozoning and Maximum Applied Water Allowance (MAWA) calculations.

California Dept. of Water Resources (water.ca.gov) · 5 steps · unrated

Enroll a certified irrigation professional or firm as an EPA WaterSense partner

epa.gov · 5 steps · unrated

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Run the EPA WaterSense Water Budget Tool to calculate a new home's landscape water allowance and requirement for WaterSense New Homes irrigation compliance.

Steps

Known gotchas

Related routes

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