The New Construction Goal: Net Zero

by Brian P. Murphy, J.D. on 2018-03-06 3:18pm


Source: Energy.gov

While the very mention of "Net Zero" may send chills up and down the spines of accountants everywhere, it is rapidly becoming the battle cry of the 21st Century green construction contractor.

"Net Zero Energy" means that a structure produces most or all of its own energy (in highly successful situations, even generating enough energy to sell back surplus to the local power grid). Wind, solar, and fuel cell generators are just some of the methods being used to create the self-contained energy-efficient structure. The technology can be applied to residential and commercial structures.

Now, "Net Zero Water" (NZW) construction is taking its place alongside Net Zero Energy with buildings designed to use as close as possible to 100% of their water from that already existing on the property and continuously recycling it along with capturing stormwater to create an entirely self-sustaining water system. The concept can be used at the building level or even expanded to be a campus-wide containment system.

Companies, governments, and organizations are increasingly aware of risks to our resources created by concentrations of population and posed by shifts in climate patterns. Building off the principles of net zero energy and climate neutrality, Net Zero Water (NZW) strategies are intended to change the way water resources are managed by making water resource planning decisions that are geared to the local conditions.

Instead of basing projected water needs on historical demand patterns, an NZW approach takes into consideration local precipitation patterns and tries to maintain a system and consumption pattern that operate at or below that available local supply. This way, rather than allowing stormwater runoff in developed areas to flow downstream, an NZW approach looks to treat and reuse runoff on-site.

What Is a Net Zero Water Building?

Source: Kohler.com


NZW means using only as much water as falls on the site in question and eliminating all water quality impacts from the site, i.e., onsite treatment, eliminated runoff. On-site treatment is a decentralized method for recycling and purifying water for reuse. Current research indicates that a significant amount of the energy used in water systems pertains to the distance that the water must travel to and from a centralized treatment system.

A net zero water building (constructed or renovated) is designed to:

  • Minimize total water consumption
  • Maximize alternative water sources
  • Minimize wastewater discharge from the building, and
  • Return water to the original water source.

NZW creates a "water-neutral" building where the amount of alternative water used and water returned to the original water source is equal to the building's total water consumption. That is:

alternative water used + water returned to original source  =  building's total water consumption

The ultimate goal of an NZW system is to preserve the quantity and quality of natural water resources with minimal deterioration, depletion, and rerouting of water. This is accomplished by utilizing potential alternative water sources and water efficiency measures to minimize or eliminate the use of supplied freshwater. A completely successful NZW building (or campus) totally offsets water use with alternative water plus water returned to the original water source.

Note: if a building is not located within the watershed or aquifer of the original water source, then returning water to the original water source is a low probability, shifting the reliance to an alternative water use to provide a successful NZW strategy.

Measuring Success

The ability to measure net zero water outcomes is important so that you can determine if your project has met the NZW objective. Using the formula provided above:

  • "Total water use" = the amount of water consumed within the boundaries of a building from all sources (potable and non-potable including freshwater and alternative water) over the course of a year.
  • "Alternative water use" = the amount of water consumed within the boundaries of a building from sustainable water sources not derived from freshwater sources over the course of a year. That is, in a net zero building, the total annual water use should be offset by alternative water in part or in full.
  • "Water returned" = the amount of water collected from the building systems (green infrastructure and on-site treated wastewater) and returned back to the original source over the course of a year. Again, in a net zero building, the total annual water use should be offset by alternative water in part or in full.

To verify that a building is attaining its goal of operating at net zero, one needs to collect annual water use data for each water flow:

  • Potable water use
  • Non-potable water use (from freshwater sources)
  • Alternative water use
  • Treated wastewater on-site returned to original water source
  • Stormwater infiltrated to the original water source through green infrastructure.

Total all freshwater use and alternative water use to calculate the building's total annual water use. Then, add alternative water use and treated wastewater and stormwater returned to the original source. If the total of this is equal to or greater than the total annual water use, then the building is considered to be a net zero water facility.

Note: If unable to monitor stormwater infiltration, you can roughly estimate by multiplying the amount of precipitation received within the boundaries of the building over the course of year by the capture capacity (area) of green infrastructure features, and subtracting any potential losses of captured water considering the infrastructure design. These may include:

  • evaporation of the captured water
  • runoff (if the green infrastructure feature only provides a percent reduction in runoff), or
  • transpiration by plant coverage.

Purdue-Whirlpool-Kohler Partnership

The ReNEWW House (Retrofit Net zero Energy Water Waste) Initiative is a partnership between Whirlpool Corp., Purdue University, Kohler Co., and others which was created to develop a world‐class research laboratory and sustainable living showcase. The partnership retrofitted an 87‐year‐old home near Purdue’s campus in West Lafayette, Indiana.

After focusing on net‐zero energy in the initial year of the project, sustainability experts from Whirlpool installed water systems that filter and reuse water throughout the home in an effort to reduce or eliminate the home's dependence on city water.

At the 2015 Greenbuild Expo, Eric Bowler, a senior engineer at Whirlpool, and Rob Zimmerman, senior manager of sustainability at Kohler, reviewed the net zero water initiatives at the home.

“We expect the ReNEWW House to provide Kohler and Whirlpool with new insights on how people use water, and the energy associated with that water, in their normal routines,” Zimmerman said. “The project will allow us to gain a deeper understanding of how our products can be improved and how user behavior can contribute to higher levels of water efficiency.”

Learn more about Net Zero Water Systems through these resources:



Brian P. Murphy, the author, is a researcher and writer for At Your Pace Online, an online provider through AYPOTech.com.