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Taking It to Zero

Net-zero-water buildings are the next generation of water conservation.

By Leah Grout Garris

Oregon Health and Science University (OHSU) Center for Health & Healing
The Oregon Health and Science University (OHSU) Center for Health & Healing has not completely achieved net zero water, but it has virtually eliminated its wastewater contribution to the municipal sewer system.

Is it possible for a building to use only the water it generates or captures on site? That concept, called net zero water, has gained increasing buzz as the International Living Building Institute's Living Building Challenge becomes more popular, says Jacob Arlein, partner and director of certification services at Environmental Building Strategies.

The Challenge is similar to LEED, but pushes the envelope further, he says. "To be certified, you need net zero water," he explains. "The industry is realizing that it must be possible."

It is a reasonable goal, Arlein says, but certain variables improve feasibility. "Net zero water may be easier for educational facilities due to larger, landscaped areas that collect more water," he says. Being located in a region with consistent, year-round rainfall also helps.

A water audit can help determine if net zero water is achievable. "Evaluate fixtures, the type of landscaping, and water bills from the past few years," Arlein says. "How much water you're using and where you're using it are important details."

Conserve First

If net zero water is the objective, start by concentrating on usage reduction. "Specify top-of-the-line, low-flow fixtures," Arlein suggests. Reducing use is easier and more cost-effective than installing reuse systems that capture and recycle stormwater, greywater, or blackwater.

Reducing irrigation -- especially for schools with large expanses of green space to maintain -- is another key step. Native plantings, xeriscaping, or smart landscape design can reduce or eliminate the need for irrigation.

Capture and reuse systems, such as stormwater harvesting systems, capture rainwater that's free for the taking (and free of salts and acids). The systems filter, sterilize, and store rainwater for applications that don't require drinking-quality water, such as urinal and toilet flushing, irrigation, and cooling tower makeup.


"The more we look into saving water, the more we realize that payback is solid -- especially if your water costs are high."


Greywater or blackwater recycling systems are also used in net-zero-water buildings. Greywater systems reclaim and treat water from sinks, laundry equipment, and shower drains. Blackwater systems treat and disinfect wastewater containing bacteria and bodily waste. In both cases, once the water is purified and filtered appropriately, it can be used for non-potable applications.

"The more we look into saving water, the more we realize that payback is solid -- especially if your water costs are high," Arlein emphasizes. He says that upgrading to more water-efficient fixtures, and even investing in greywater or blackwater systems, can positively impact the bottom line and offer a faster return on investment than some energy-efficiency measures.

Zero in Action

Although the Oregon Health and Science University (OHSU) Center for Health & Healing hasn't completely achieved net zero water, it uses many of these technologies to lessen impact on the city sewer system, reduce water expenses, and reuse available water. Beyond municipal resources, the building gets its water in three ways:

  1. Rainwater harvesting
  2. Groundwater harvesting from basement de-watering (the building's lower levels are below the Willamette River level)
  3. A membrane bioreactor for on-site capture, treatment, and reuse of blackwater

The OHSU Center for Health & Healing has virtually eliminated its wastewater contribution to the municipal sewer system. "We create top-grade, non-potable water for flushing toilets, irrigation, condensing cooling tower makeup, and some of our closed loops," says Troy Potter, director of engineering operations for the OHSU Center for Health & Healing with CBRE, the building's property manager.

Besides a few clinical spaces that require traditional fixtures, the building's fixtures are low-flow and hands-free. Potter says hands-free faucets help reduce water wasted by occupants who forget to turn off the water. These fixtures contribute to a 40 percent water use reduction compared with a base building. Five rooftop gardens planted with mostly hearty, native vegetation require little to no irrigation.

"OHSU wanted to do the right thing -- not only get LEED Platinum certification, but reduce our impact on the city sewer," says Dyann Hamilton, CBRE's alliance director of building and project management services for the OHSU Center for Health & Healing. "We're creating a self-sustainable situation so we're not a burden on city resources."