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Stormwater BMPs

Graywater Harvesting and Carbon Footprint

The UK’s Environment Agency created quite a stir among some sustainability professionals (self included), when they published statements like: “Buildings using harvested rainwater or treated greywater typically increase greenhouse gas emissions compared to using mains water,” in their report Energy and carbon implications of rainwater harvesting and greywater recycling (2010).

The report sparked great debate on what the report claims and also what it means for us to pursue better and more energy-efficient strategies at a minimum. It is important to recognize that the study is UK-centric. Geography, geology, and climate can make tremendous impact on the energy intensity or carbon footprint on main water: the numbers need not add-up the same for all communities across the world, but still the report may warn us not to make automatic assumptions about energy conservation just because we deem a particular technology otherwise “sustainable.” Moreover, before jumping to too many conclusions, please also heed this disclaimer-like statement in the Executive Summary:

“This study focuses on the energy and carbon implications and mains water savings of rainwater and greywater systems that supply water for non-potable use in buildings and are commercially available in the UK. It does not include any other environmental, social or economic costs and benefits assessment. Emerging gravity-fed rainwater systems, and all systems exclusively supplying water for external uses, including rainwater butts, have not been considered in this study.”

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