Green-Gray Assessment: How to Assess the Costs and Benefits of Green Infrastructure for Water Supply Systems

Healthy watersheds and forests play a vital role in water supply infrastructure systems. They can store and moderate water flows and help purify water, which can reduce water treatment and dredging costs, and avoid costs of supplementing water supply from other sources. Healthy watersheds also provide a variety of important co-benefits for society. But how much value do watersheds provide from system to system?

WRI’s Green-Gray Assessment methodology allows stakeholders to assess the costs and benefits of integrating green or natural infrastructure into water supply systems. This methodology provides three preassessment steps and six main analysis steps rooted in policy appraisal tools familiar to water suppliers. The methodology report also provides recommendations on how to present results to increase decision-uptake with water suppliers and other key stakeholders. It has been used for multiple cities around the world, with more assessments currently underway.

Erin Gray, Suzanne Ozment, Juan-Carlos Altamirano, Rafael Feltran-Barbieri, Ana Gabriela Morales