Sink-to-Yard Graywater Retrofit Could Make Desert Bloom

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sink-to-garden.Researchers at New Mexico State University are testing a relatively inexpensive plumbing retrofit that could help buildings capture relatively clean graywater from plumbing before it hits the sewers, and reuse it onsite for outdoor watering.  It’s a green four-for-one: the NMSU graywater system conserves water, relieves sewer systems of excess flow, fosters tree growth to cool buildings, and reduces stormwater runoff by improving soil and vegetation.

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Graywater Recycling is the Wave of the Future

Graywater generally refers to water from buildings that does not come from toilets (that’s considered blackwater).  Graywater comes from bathroom sinks, showers, bathtubs, dishwashing machines, clothes washers, and practically any other fixture into which humans do not normally relieve themselves.

For some purposes, kitchen sinks are considered blackwater sources because of the grease and meat scraps they contribute to the wastewater flow.  If you use cloth diapers and wash them at home, your laundry machine may also be considered a blackwater source.

Graywater Recycling in New Buildings

New green buildings ideally include a customized system for separating graywater from blackwater.  Graywater recycling systems also are perfect for low-income housing because they help keep operating and utility costs down.  In urban areas, recycled graywater can be used to flush toilets rather than for grounds keeping.

Designers are also beginning to explore the concept of plumbing fixutres that have built-in graywater recycling capabilities, such as a clothes washer that supplies used water directly to a toilet.

Graywater Recycling in Existing Buildings

Installing a graywater recycling system in an existing building can involve an extensive plumbing retrofit, which is beyond the financial reach of many individual households.  NMSU has an answer for that.  Their research is focused on a remote-control system that can be installed in existing plumbing.  They are working with a company called Aquaverde, Inc., that has developed a graywater recycling system that uses radio signals to detect activity in blackwater fixtures.  When the blackwater fixtures are inactive, a valve diverts graywater to a collection tank.  When the sensors dectect blackwater activity, (for NMSU’s purposes, kitchen sinks are included) the flow goes to the sewer line.

Graywater Recycling – Problem Solved?

If the Aquaverde system proves cost-effective, it could potentially put graywater recycling in the hands of millions of ordinary homeowners.  The system does require energy to run a pump, which could be offset individually by simple energy conservation measures, or with solar or other alternative power.  The increased energy demand could also be offset on a macro level, taking into account the reduced demand on water supply and sewage treatment systems in a given area.

Energy and plumbing costs are not the only limitation, though.  A truly mass shift toward onsite graywater recycling would require some additional adjustments – and that’s a good thing.

Building owners and occupants would need to pay more attention to everything they pour down a drain – after all, it’s going to end up in their community, not miles away .  Graywater recyclers would need to focus more of their purchasing on eco-safe detergents and household cleansers, natural shampoos and other personal grooming products, and chemical-free foods.  We could also see more attention on keeping medications and do-it-yourself products out of building drains- and that’s another good thing.

Image: merelymel13 at flickr.

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Tina Casey

Tina specializes in advanced energy technology, military sustainability, emerging materials, biofuels, ESG and related policy and political matters. Views expressed are her own. Follow her on LinkedIn, Threads, or Bluesky.

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