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The International Living Future Institute and the Cascadia Green Building Council are applying the net-zero concept to water use. In their “Toward Net Zero Water” report , for example, the organizations encourage builders to operate within their “water budget” through the integration of closed-loop systems that emphasize water efficiency, as well as on-site supply, treatment, and reuse.

And while there has been a lot of focus on use-based systems such as rainwater harvesting and gray water reclamation, there is another side of the water cycle that needs to be addressed—wastewater treatment. Although we tend to quite literally forget about water once it is flushed down the toilet, recent research shows that green builders should be considering community- and even site-level wastewater treatment systems.

In the report, “Clean Water, Healthy Sound,” the Cascadia Green Building Council used life-cycle analysis to evaluate the environmental impacts of four different community-based wastewater treatment systems in comparison to our current conventional, centralized wastewater infrastructure.

Their findings confirmed that low-energy systems such as composting toilets and constructed treatment wetlands offer significant advantages over our existing centralized wastewater infrastructure. Composting toilets, for example, had 44% less impact on global warming, and constructed treatment wetlands had 6% less impact on ozone depletion.

“We’re not advocating that a city rip out its infrastructure and put in wetlands, as much as we are doing this so we can help inform … what kinds of systems make sense,” notes Kate Spataro, one of the authors of the report. “This research helps provide some interesting data and support for developers, architects, and builders to use not only with their clients, but with the regulatory agencies that they might need to have discussions with in order to make these kinds of systems a reality on their projects, as well as with designers they are working with.”

Spataro says the treatment side of the water cycle is something green builders—as well as homeowners—need to think about if we are truly going to move toward “net-zero” water. “We flush a toilet, and water goes down a drain without a connection to what happens with that water after it leaves our homes,” Spataro says. “We need to start treating our water and our waste in a different way because it really helps us use water wisely. For every gallon we use, we know we also have to do something to get rid of it.”

You can view the executive summary of “Clean Water, Healthy Sound” here .