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Aerial view of an estuary with a web of blue streams flowing through a chartreuse-colored island and into a bright blue bay

WEAP (Water Evaluation and Adaptation Planning) is a software tool for integrated water resources planning. It provides a comprehensive, flexible and user-friendly framework for policy analysis.

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Last updated on 14 November 2025

Many regions face formidable freshwater management challenges. Allocation of limited water resources, environmental quality and policies for sustainable water use are issues of increasing concern. Conventional supply-oriented simulation models are not always adequate.

Over the last decade, an integrated approach to water development has emerged that places water supply projects in the context of demand-side issues, water quality and ecosystem preservation and protection. WEAP incorporates these values into a practical tool for water resources planning.

WEAP is distinguished by its integrated approach to simulating water systems and by its policy orientation. WEAP places the demand side of the equation – water use patterns, equipment efficiencies, reuse, costs and allocation – on an equal footing with the supply side – streamflow, groundwater, reservoirs and water transfers. WEAP thus provides a laboratory for examining alternative water development and management strategies.

WEAP is comprehensive, straightforward and easy-to-use, and attempts to assist rather than substitute for the skilled planner. As a database, WEAP provides a system for maintaining water demand and supply information. As a forecasting tool, WEAP simulates water demand, supply, runoff, streamflows, storage, pollution generation, treatment and discharge, and instream water quality. As a policy analysis tool, WEAP evaluates a full range of water development and management options, and takes into account multiple and competing uses of water systems.

To see a full list of publications that use WEAP – including those produced outside of SEI – see the publications page of the external WEAP website.

David Purkey

Senior Research Fellow

SEI Latin America

Doug Chalmers

Scientist

SEI US

Laura Forni

Water Program Director

SEI US

Profile picture of Annette Huber-Lee
Annette Huber-Lee

Senior Scientist

SEI US

Profile picture of Brian Joyce
Brian Joyce

Senior Scientist

SEI US

Profile picture of Jack Sieber
Jack Sieber

Senior Scientist

SEI US

Profile picture of Charles A. Young
Charles A. Young

Senior Scientist

SEI US

Anne Hereford

WEAP and Operations Associate

SEI US

Marina Mautner

Senior Scientist

SEI US

Romina Díaz-Gómez

Scientist

SEI US

Samara Saquib

Analyst

SEI US

Andrea Carlos-Carlos

Associate Scientist

SEI US

WEAP history and highlights

WEAP user testimonials

WEAP 50K celebration: 2024

WEAP tutorials in English

Tutoriales WEAP en Español


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