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Net zero water

Water and climate change are inextricably linked. As the planet warms, weather patterns will shift, exacerbating drought in some areas and delivering more rainfall to others. Water itself requires energy to deliver, so excess use compounds our energy problems. And many renewable sources of power, such as solar, require massive amounts of water as an input, creating further pressure on limited resources.

Net zero water is an analogous concept to net zero energy. Through a combination of rainfall harvesting, aggressive conservation, and water recycling, buildings can achieve self-sufficiency from the water “grid.”

At least in theory. Net zero water is considered the most difficult condition in the Living Building Challenge, an uber-stringent standard for green buildings. Despite a handful of attempts, no buildings have yet achieved LBC certification.

To achieve water independence, buildings divide available sources of water into categories and treat them accordingly. Rainwater is relatively clean, and can be converted into drinking water with a minimum of processing.

Grey water can be cleaned by filtering it through a biological wastewater treatment system such as the Living Machine, a sort of wetlands in a box containing plants, bacteria, plankton, even snails and clams. I’ve seen a similar principle put in place at one of the landfills I visited for TerraPass. Effluent from the landfill was bubbled through a series of plant-filled pools, in which organisms remove contaminants such as organic matter and heavy metals. By the time the water reaches the final pool, it is clean enough to be reintroduced into the watershed.

It’s unclear what role, if any, the net zero water concept will play in future conservation efforts. In the most water-starved parts of the country, homes undoubtedly do not receive enough rainfall to serve their needs. And the most resource-efficient parts of the country – large cities – will always have to import water, because of their sheer density. Nevertheless, water efficiency makes as much sense as energy efficiency, and net zero water provides an admirably ambitious goal.

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