Quenching the Built Environment's Thirst for Water

Designers deploy synergistic strategies to decrease demand and find new sources of supply

Joann Gonchar, AIA

Not so long ago, water conservation took a back seat to energy efficiency in the world of green building. But that seems to be changing as designers, building owners, and the public become increasingly aware of pressures on freshwater supplies.

Perhaps this is due to the news of dwindling reservoirs, water rights wars, and limits on use that appear in the media with alarming frequency. California is in its third consecutive year of a drought that has hit the state's agricultural industry particularly hard and has prompted many districts to impose water restrictions. For the Southwest as a region, some long-term predictions are especially sobering: Lake Mead, which supplies water to millions of people, has a 50 percent chance of running dry by 2021, according to a recent study from the Scripps Institution of Oceanography. In the Southeast, the drought conditions of the past few years have eased, but Georgia is still in the midst of a two-decade-long battle with Alabama and Florida over Lake Lanier, a reservoir built primarily for hydropower generation and flood control that is now the source for almost all of metro Atlanta's water supply.

An intimate link
Conservation is especially critical in water-stressed parts of the country, but regions not prone to shortages can also benefit from its methods. One reason is the often overlooked connection between water use and energy production. Studies quantifying the relationship between the two resources are limited, but according to an estimate by the Electrical Power Research Institute, about 4 percent of power generation is used for moving and treating water and wastewater nationwide. Water use also has a corresponding tie to greenhouse-gas production. The River Network, a nonprofit organization focused on preserving freshwater sources, calculates that the carbon dioxide associated with moving, treating, and heating water is 290 million metric tons annually, or about 5 percent of U.S. carbon emissions.

Kroon Hall at Yale University has a storm-water treatment and reuse system that collects runoff from the building�s roof and green spaces and directs it to irrigations and toilet flushing. The system, along with water-conserving plumbing fixtures, is expected to save 500,000 gallons of water each year.

 

Electricity production is also highly dependent on water. Thermoelectric power plants (those that rely on fossil fuels, biomass, or nuclear energy) withdraw about 25 gallons of freshwater for every kilowatt of electricity generated, according to the U.S. Department of Energy.

In buildings, plumbing-fixture selection is an important component of water efficiency. And trends like the growing rigor of the popular rating system, the U.S. Green Building Council's Leadership in Energy and Environmental Design (LEED), are pushing design teams to choose fixtures that consume less water. Before the latest version of the rating system launched in late April, projects could earn one point toward certification by reducing indoor water use by 20 percent when compared to baseline fixture requirements. But under the new system, this savings level becomes a prerequisite: Projects earn no points for satisfying this performance minimum, but those that do not comply are ineligible for certification. In addition, the baseline for some fixture types has become more stringent. For example, allowable flow rates for lavatory faucets in public buildings have decreased from 2.5 gallons per minute (gpm) to 0.5 gpm.

Fixture selection is, of course, only one part of the water conservation picture. Project teams should also consider other methods for reducing demand, including specifying water-efficient appliances and other process equipment, and designing landscapes that are less dependent on irrigation. But after chipping away at demand, architects and their consultants should examine the water supply: Buildings in North America typically rely on only the highest-quality water for all applications, including drinking, bathing, irrigation, and flushing toilets. However, where regulations allow, water that may not meet potable standards can be substituted for some of these uses.

Water and the land
Especially in nonarid climates, an obvious alternative source is the water that falls from the sky. And combining rainwater collection and reuse strategies with low-impact development techniques, such as green roofs, permeable pavement, and rain gardens, can help resolve storm-water-control problems, points out Stephen Benz, a civil engineer and principal at Sasaki in Watertown, Massachusetts. By considering these issues in tandem, "you end up with good synergy between rainwater and storm-water solutions," he says.

One project that takes a coordinated approach to water conservation, rainwater harvesting, and site development is Kroon Hall, an academic building for Yale University's School of Forestry and Environmental Studies (F&ES) in New Haven, completed in May and on track for LEED Platinum certification. Designed by London-based Hopkins with the Connecticut firm Centerbrook Architects, Kroon consolidates staff offices and other F&ES facilities that had been previously scattered among nine buildings. The long and thin building sits between a pair of L-shaped neo-Gothic structures on a site that had been occupied by a long-defunct power plant and parking lots with impervious pavement. But now, the new and old buildings define a pair of grassy courtyards that help transform the previously almost industrial site into an inviting series of outdoor spaces and play an integral role in Kroon's water-conservation and storm-water-mitigation strategies.

1. Kroon Hall 2. North courtyard 3. Service courtyard 4. Filtration pond

 

From the building's southern courtyard, which is essentially a ground-level green roof built atop new loading docks and other services, an underground tank collects runoff and slowly discharges it, lessening the burden on New Haven's combined sewer system. From the roof and the northern courtyard, a rainwater-harvesting system collects runoff and channels the so-called "first flush" - the first inch of rain that falls during a storm - through a filter that removes particulate matter such as leaves, insects, or dirt. Then, all of the water from the roof and northern part of the site, both filtered and unfiltered, empties into a water feature filled with native wetland plants such as cattail, iris, and lotus. The plants, which remove impurities, including nitrogen and phosphates, help make the pond into "a machine for treating water and an asset to the landscape," says Cricket Brien, an associate at Philadelphia-based OLIN, the firm responsible for Kroon's landscape design. From the pond, the treated water is directed to storage tanks and used either in irrigation or toilet flushing.

Kroon's runoff cycles through a water feature (top) containing native wetland plants (below) that remove impurities such as nitrogen and phosphates. Photo: © Robert Benson (top); courtesy Olin (bottom)

 

The project team estimates that the rainwater-harvesting and site-design strategies, in combination with water-conserving plumbing fixtures, will result in a 75 percent reduction in potable water use when compared to a standard building, or a savings of about 500,000 gallons per year.

Refuse to resource
Rainwater is not the only source of reclaimed water suitable for nonpotable applications within buildings. A few institutional and commercial buildings treat and reuse on-site-generated wastewater. One such project is the 351-bed dormitory under construction at Emory University in Atlanta, which will include a system for recycling graywater (wastewater generated from nonindustrial processes such dishwashing, bathing, and laundry, and excluding water from kitchen sinks and toilets). The dorm, designed by Ayers/Saint/Gross and slated for completion in 2010, will capture shower and lavatory water and will use it for toilet flushing after filtering and chlorination with sodium hypochlorite. The system is expected to save 1 million gallons of potable water annually.

Another type of on-site wastewater treatment, known as an a "Eco-Machine," mimics nature and relies on beneficial bacteria, plants, fish, and other organisms to break down and consume pollutants in water. A recently installed Eco-Machine at the Omega Center for Holistic Studies, in Rhinebeck, New York, replaces the 195-acre campus's traditional septic tank and leaching field system and can handle both graywater and blackwater (sewage) from 700 guests, or 52,000 gallons each day.

In a cycle that takes about two and a half days, the Omega wastewater travels through a system that includes underground anaerobic tanks, constructed wetlands, and aerated lagoons. Along the way, contaminants such as nitrates and ammonia are removed. The process also greatly reduces levels of total suspended solids (TSS) and biological oxygen demand (BOD). Both are measures of water quality, but TSS refers to suspended material in water, either organic or inorganic, while BOD refers to the rate of uptake of dissolved oxygen and is an indication of the presence of organic material, explains Jonathan Todd, president of Woods Hole, Massachusetts-based John Todd Ecological Design, the Omega system's designer.

The Omega Center for Sustainable Living has a south-facing glass facade (above) with an integrated sunshade. It provides the sunlight that the aerated lagoons' plants need to thrive while protecting them from direct solar exposure in the summer. Photo: © Andy Milford
	LEFT 1. Below-grade septic tanks 2. Below-grade anaerobic tank 3. Constructed wetland 4. Aerated lagoon 5. Sand filter 6. Parking/subsurface dispersal 7. Rain garden 8. Below-grade cistern         BOTTOM 1. Photovoltaic panels 2. Mechanical/ electrical room 3. Green roof 4. Aerated lagoons 5. Constructed wetlands

 

At Omega, a new building, the Center for Sustainable Living, houses part of the treatment process and has a classroom and a small lab where the institute plans to teach guests, students, and the public about the filtration system, the water cycle, and sustainable design. The institute hopes the center will achieve certification under the Living Building program created by the Cascadia Green Building Council to encourage construction of self-sustaining facilities. To that end, the center includes several tightly coordinated features, such as photovoltaics that supply all of the power necessary for operation and an integrated set of landscape and water systems. "The building is basically a pedagogical tool," explains Laura Lesniewski, AIA, a principal at Kansas City, Missouri-based BNIM, the center's architect.

The Omega building houses aerated lagoons where the roots of wetland plants act as habitat for microbial populations that scrub the water. Photo: © Andy Milford

Inside the center, toilets are flushed with roof runoff stored in an underground, 1,800-gallon cistern, while the toilets elsewhere on the campus rely on well water. Omega plans to collect operations data and apply for a reuse permit so that it can eventually implement a closed-loop system, with the Eco-Machine supplying water for toilet flushing and irrigation campuswide. But for now, the clean Eco-Machine water infiltrates the aquifer that sits below the Omega property and feeds a nearby lake. Rainwater falling on the site follows a similar path, first traveling through an integrated system of bioretention swales, rain gardens, and wetland cells. The strategies ensure that storm water, along with Eco-Machine-treated water, reaches the lake much cooler and cleaner than surface runoff would, according to Tom Price, a principal for Omega's landscape architect, Conservation Design Forum, in Elmhurst, Illinois. The temperature of the water is important for the flora and fauna living in the lake and for the surrounding wetlands, he explains.

Across the continent, on Vancouver's waterfront, the recently completed 1.1-million-square-foot expansion to that city's convention center has a treatment system hidden in its base that directs blackwater to toilet flushing and to irrigation of a 6-acre green roof. But instead of an Eco-Machine, designers chose a process that relies on a membrane bioreactor, ultraviolet light, and activated charcoal, partly because of space constraints and structural issues. An Eco-Machine's plants require sunshine, so the likely spot for its tanks would have been the roof - a problematic configuration in a seismically active zone, points out Blair McCarry, a principal in the local office of Stantec, the project's m/e/p engineer. "The secondary costs became prohibitive," he says.

Designers took advantage of the Vancouver Convention Center's site on the harbor by incorporating seawater into several of the expansion's building systems, including the blackwater treatment system (below), which has desalination backup. The treated blackwater is used to flush toilets and irrigate the convention center's 6-acre green roof. According to the project team, it is the largest nonindustrial planted roof in North America. Photos: © Vancouver Convention Center

Since the supply of wastewater will vary with occupancy, the convention center system has several backup options for toilet flushing and roof irrigation, including the municipal blackwater and potable water systems. It also has an on-site desalination plant. Although removing salt from water can be an energy-intensive process, here it makes sense because the site is on the harbor, says Tom Burgess, AIA, project manager for Seattle-based LMN, the expansion project's design architect. The building also has a seawater heat-pump and cooling system and a seawater fire-suppression system. "Because the building is over the water, we are taking advantage of it," he says.

Beyond toilets and irrigation
Uses for nonpotable water are not limited to toilet flushing and irrigation. In a recently completed project for Southface Energy Institute, an Atlanta-based nonprofit that promotes construction of sustainable homes and workplaces, harvested rainwater is used for these typical applications but is also incorporated into the operation of the cooling system.

The Eco Office, an addition to the Southface Energy Institute's headquarters in Atlanta, has rooftop and underground cisterns that store storm-water runoff from a photovoltaic array and a green roof. The water is used for both toilet flushing and irrigation, and is part of the operation of the mechanical system. Photo: © Jonathan Hillyer

 

The 10,000-square-foot, LEED Platinum building, dubbed the "Eco Office" because it is intended to demonstrate technologies appropriate for commercial construction, is an addition to a demonstration home built by the organization in 1996. The new structure, designed by Lord Aeck & Sargent, has a dedicated outdoor air system (DOAS) with a multistage evaporative cooler that makes use of harvested rainwater to help reduce the temperature of incoming air without adding humidity, explains Gregory Jeffers, a senior project engineer with local firm McKenney's, the mechanical system's design-builder. A spray system surrounding the building's rooftop heat pumps also relies on harvested rainwater and creates a cool microclimate around the equipment, enhancing its efficiency. The technology is one of several integrated energy-conserving strategies that should help the Eco Office exceed the performance of a code-compliant building by 53 percent.

In addition to serving as a consumer of salvaged water, mechanical systems can also provide a source of water that can be directed to nonpotable uses inside a building or on its grounds. One such source is the condensate produced by air-conditioning equipment, especially in hot, humid climates. Condensate is sometimes used directly within the mechanical system, as makeup water in cooling towers, or for flushing toilets or irrigation.

Somewhat surprisingly, condensate collection was not an appropriate strategy for the Eco Office project, despite Atlanta's hot and sticky climate. The building's unconventional cooling system makes little condensate, according to Jeffers. "Typically, the more energy-efficient a system is, the less condensate it produces," he says.

For Southface, as for almost any project that relies on thermoelectric power, this energy efficiency translates into water savings well beyond the confines of the building. Since electricity generation requires water, "we're not just saving resources locally, we're saving them regionally," says Jeffers.