Net zero water

Written by adam


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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  1. Tom Glendinning

    Toilets are the largest necessary residential consumers of water. Three uses per day in a four person household adds up to about sixty four gallons.
    Low flow commodes do not remove the brown trout with one flush or leave residue in the bowl.
    Composting toilets provide the answer to many issues, especially in a municipal system where effluent goes to a water course: stream, river, lake, ocean.
    Solid waste is managed on site.
    No water pollution.
    Water use reduced.
    Waste can be recycled by use of the compost produced.
    Waste volume is reduced.
    Clean out is a rare event.
    I do not use more than 15 gallons per day average in a one person household with a Clivus Multrum, low flow shower head with cut off. The Clivus was installed in 1976 and has been cleaned out four times.
    Thank you, Abby Rockefeller for introducing the Clivus Multrum to the USA. They are mainly sold to park systems now. The health departments caused too many permit problems for mainstream adoption in residential and commercial use.
    Thye modified lagoon system is expensive and complicated to operate. Further, why were the lagoon systems serving cities along the Mississippi river condemned by environmentalists who, now, proclaim the residential use benefits of this system?
    In the words of Arsenio Hall, “Makes you want to go Hmmmmmmmmmmmmm.”

  2. D Schowe

    How about a system for home use that recycles shower, bath and laundry water and uses it to flush toilets. There is no need to process it (dirty water in-dirty water out), just a storage system. Although energy would be required to pump to storage.

  3. Angie

    It would be great if the illustration were larger. I can’t read it and enlarging it causes it to blur even more. Does anyone have a scalable version?
    I think this idea is great and along with other methods could be a wonderful solution for a house I plan to build. While the article is brief, it is a good reminder to look for additional resources like books and other articles.

  4. gatcheson

    Going to net zero water usage seems unnecessary for society in general: modern sanitation is the single greatest lifesaving technology. Ever. We already have the infrastructure for delivering clean water and treating the waste. We just have to reduce the demand to keep within the present capabilities. Except parts of the southwest, where I do not think there is a solution except some people moving away.
    Kohler just gave me a propaganda speech on their water saving fixtures, and they are really amazing. Especially as they push from standard 1.6 gpf toilets down to 1.28 and 1.0 to meet LEED standards.

  5. Jack

    I recently installed two low flow (1.6 gpf)toilets (Jan 09 an American Standard Champion 4 and Sep 09 an American Standard Cadet 3) to replace two American Cadet pre-1992 toilets). Neither toilets leave reside most of the time. I am very pleased with the flush performance of both toilets.

  6. Eden

    It is worth noting that there are now three completed projects that are in their verification year (required for certification under the Living Building Challenge): Tyson Living Learning center in Eureka, Missouri; Omega Center for Sustainable Living in Rhinebeck, New York; and Eco-sense, a private residence in Victoria, British Columbia.
    There are more than 60 project across North America (and beyond) that are either in design or construction phases pursuing the Challenge. The program is young – launched in November 2006. Even in the best of design and construction circumstances, this is a tight window to complete any project, let alone a Living Building.

  7. Bill Worthington

    Your suggestion of re-using grey water to flush toilets seems to make sense, though I suspect the comparative volumes don’t quite balance. When I was stationed at Thule AFB (1956) our building had such a system. It was awful because the grey water stank so bad that we would always try to schedule our use to another building where they had indoor privies with air-flow. I suspect that some kind of filter/reactor would be advised.

  8. JZ

    And then you have the issue of figuring out what would work for skyscrapers and apartment complexes in a place like New York City.

  9. Ed

    A sticking point: If people use less water, local governments make less money.
    Example: To conserve water, the South Florida Water Management District (SFWMD), which manages water for 5 million people, plus agriculture and the Everglades, instituted twice a week lawn watering. But then local governments threatened to sue the SFWMD: revenues were falling because people were using less water. So now you can water three times a week.
    Last year, when it was reported that Celine Dion’s 5.7 acres consumed 6.5 million gallons, a local official said, “Since they have larger properties with an abundance of vegetation – ideal for ensuring privacy, which is of special importance to well known personalities – it looks like higher-than-usual water usage. In reality, per acre, it’s only a little above average.”
    Tiger Woods’ property was in second place: 3.7 million gallons.