Design Professional’s Guide to Onsite Water Use and Reuse: a Preview

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“The amount of water on our planet has not changed for millennia. What has changed is our need for it. Our increase in the use of fresh water resources is quickly outstripping our ability to channel the amount of fresh water we need, where we need it, when we want it. Sound like a design problem? It is.”

So wrote Bill Worthen, FAIA, in the January 2014 issue of ARCHITECT magazine. At the time, Worthen was the Founding Principal of the consultancy Urban Fabrick, which he had established in 2005 to “make sustainability accessible and engaging to all.” High on his agenda was development of a professional guide that addresses water use and reuse in buildings.

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The idea of doing practice guides stemmed from Worthen’s time as Director, Resource Architect for Sustainability at AIA National, where he oversaw the development and publication of An Architect’s Guide to Integrating Energy Modeling in the Design Process. He recognized not only that energy modeling was a best practice for resource conservation, but also that it was becoming a required means of introducing non-prescriptive responses to building code energy criteria. He also understood that the majority of AIA members—and architects more generally—represent small- and mid-size firms that often lack the technological depth of large firms. The guide thus was conceived as a resource that would enable all architects to employ energy modeling not only as a technical tool, but also as a design tool.

The Design Professional’s Guide to Onsite Water Use and Reuse, scheduled for publication in mid-2017, is similarly conceived as a design resource for architects, written in language that can be easily understood by—and thus shared with—clients, building owners and operators, and the public at large. To do so, Worthen and his colleagues Kyle Pickett and Brett Rosenberg have assembled a team of industry professionals from around the US, including architects, landscape architects, engineers of various disciplines, and policy experts.

The development and production of the guide is made possible by support from the Charles Pankow Foundation, Google, AIA California Council, Magnusson Klemencic Associates, WE&RF, and the City of Santa Monica. This funding was secured through the establishment of a nonprofit corporation, the Urban Fabrick Collaborative, to “conduct research and create inclusive outreach initiatives on the planning, design, construction, performance and beauty of the built environment.”

Bill Worthen passed away unexpectedly in January 2017. In his honor, The Urban Fabrick Collaborative will soon be repositioned as The William J. Worthen Foundation, a nonprofit committed to communicating the value of community, sustainability and collaborative design. The Design Professional’s Guide to Onsite Water Use and Reuse will be one of the many elements of his legacy.

The guide will cover the importance of non-potable water reuse in the context of increasing demand and changing weather patterns, integrated water management, appropriateness for different building projects, the impact of water reuse on design, the techniques and components of reuse systems, and strategies for advocacy and permitting—supported by case studies, technical references, and other resources. It will serve as the basis for a variety of continuing education offerings by AIA and USGBC components and others. As a preview, we offer here an extract from the chapter on what you need to know to design, build and operate a system. Stay tuned for more.

Non-Potable Water Reuse Guide: an excerpt

Water Treatment Steps
Most successful water reuse systems, regardless of water source and reuse application, include three basic steps: pretreatment, treatment, and polishing.

Primary: Pretreatment
Potential water sources from rainwater to graywater to wastewater all require a pre-treatment step to remove non-biological material in the water, coarse biological material, or fatty biological material that may be difficult to remove in the subsequent treatment steps.

As there is inherent variability in most potential water sources, pretreatment often also includes some form of flow equalization, to buffer diurnal, seasonal, or stochastic variability. This allows adequate supply for reuse applications but also reduces the cost and increases the effectiveness of subsequent treatment steps.

Secondary: Treatment
Most potential water sources include at least some organic material that is dissolved or in particles too small to be removed in the pretreatment step. Left in the water, this organic material will cause “septic” or odor-generating conditions. Suspended solids and dissolved organics will also cause discoloration of the water.

Microbiological processes naturally consume the dissolved organic material. A wide variety of biological treatment processes exist that “turbo-charge” natural microbial processes by adding additional oxygen and by increasing the concentration of helpful treatment microorganisms. These processes can also be utilized to remove nutrients such as nitrogen and phosphorus that might to detrimental to certain to reuse applications.

Tertiary: Polishing
While the first two steps are essential for most water reuse projects, the polishing step is highly application-specific, depending on water source, reuse applications, and regulatory requirements. Polishing steps include:

Filtration. Filtration is utilized to remove suspended solids. A wide variety of media and membrane filters exist to reduce residual solids to required levels. Filtration can generally be classified as microfiltration (

Disinfection. Biological treatment and filtration can significantly decrease the concentrations of potential pathogens in reuse water, but disinfection processes are necessary to assure the high levels of pathogen removal required for certain applications.

Three main disinfection practices are commonly employed. Ultraviolet disinfection uses light of a specific spectrum to destroy the DNA of pathogenic organisms. UV systems are energy efficient and cost effective but rely on adequate biological treatment and filtration to be effective, as suspended solids can block UV radiation and shield pathogens.

Ozone disinfection systems dissolve gaseous ozone into water to degrade pathogens. Ozone is less sensitive than UV to the breakthrough of solids and can also remove residual color; however, it needs to be combined with ozone destruct systems, which remove any unused ozone gas that could be harmful or flammable.

Neither UV nor ozone provides a disinfection residual that prevents the re-growth of pathogens in reuse storage tanks or reuse distribution systems. Chemical disinfectants such as chlorine are commonly combined with UV or ozone disinfection systems to provide the needed residual effect.

Chlorine is typically used in conjunction with other disinfection technologies to reduce chemical requirements and improve overall disinfection reliability. Chlorine in excess of 2ppm can be harmful to some distribution piping and reuse applications.

Deionization. Inorganic mineral constituents such as salts can also impact reuse. Soil structure, plant communities, plumbing fixtures, and heating and cooling systems can all be adversely affected by high salt concentrations. A variety of technologies provide deionization or desalination of water, but reverse osmosis (RO) is the most common approach employed for decentralized systems. RO systems use a semipermeable membrane to remove ions (salts) from water. Pumping energy is utilized to force water through the fine membrane pores. Typical recovery rates are between 75% and 80%, with the salt solutions rejected as “brine.”

Membrane capacitive deionization (CapDI) is an emerging technology with potential for decentralized reuse applications. CapDI utilizes an electric current and ion-selective membranes to preferentially remove salts from the water, instead of forcing all flow through the membrane. Reversing the electric charge allows salts to be removed from the membranes and flushed out as brine. This process does not remove all of the salts, as RO does, but it uses less energy.

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Tim Culvahouse, FAIA

Tim Culvahouse, FAIA, is Editor-in-Chief of the AIA California Council and an architect specializing in the public communication of design ideas through his firm, Culvahouse Consulting.

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