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How Water Works for LEED
Most environmental news today from mainstream media focuses on climate change and the role of greenhouse gases produced by an increasingly industrialized world. When water issues are discussed, it is often in the context of bottled water’s negative impacts or cross-border water rights battles, rather than the importance of water efficiency in buildings.
Most estimates place the amount of freshwater — the water needed for drinking, industry and sanitation — at about 2.5 percent of the world’s total. Of that, only one-third is easily accessible to humans via lakes, streams and rivers, and more than half of it is being captured. Demand for freshwater is rising quickly, and if current trends continue, experts project that demand will double in the next 30 years.
Because water is one of the world’s most vital natural resources, all building projects — especially green projects — should include water efficiency as a goal. The good news is that significant water efficiency improvements over conventional practice are readily achievable. To obtain many of these improvements, though, facility executives should plan early, especially if LEED certification is a goal.
Water in LEED
LEED for New Construction addresses new construction and major renovation of commercial and institutional projects. Performance is evaluated in five environmental categories, one of which is Water Efficiency. LEED is a point-based system administered by the U.S. Green Building Council, with points awarded for meeting the specific requirements of credits in each of the categories.
Of the 69 possible points in LEED, only five are directly associated with water efficiency. These five points are apportioned among three LEED Water Efficiency credits:
- Credit 1 – Water-efficient Landscaping, two points
- Credit 2 – Innovative Wastewater Technologies, one point
- Credit 3 – Water Use Reduction, two points
Some water efficiency technologies and strategies can easily be incorporated at any point in the design process, or even late in the construction process, while others require early planning and integration of multiple disciplines. Understanding the requirements for each Water Efficiency Credit, as well as the design strategies for meeting those requirements and the planning process necessary to successfully develop and incorporate those strategies, is critical to optimizing water efficiency on LEED projects.
The intent of the Water-efficient Landscaping credit is to “limit or eliminate the use of potable water, or other natural surface or subsurface water resources available on or near the project site, for landscape irrigation.” One point is awarded for a 50 percent reduction in water consumption for irrigation from a calculated mid-summer baseline case, and a total of two points are awarded for a 100 percent reduction.
The optimization hierarchy for cost-effectively reducing resource consumption involves reducing demands, then meeting demands efficiently, and finally greening the supply of any residual, reduced demand. In the case of irrigation water, reducing demand can be achieved through implementation of a water-efficient landscaping design. Grouping plantings based upon irrigation requirements, minimizing water-intensive turf grass areas, and selecting plant species adapted to the climate conditions of the site are all strategies that will reduce the amount of irrigation water required compared with a conventional, water-intensive landscape design. These strategies alone may be sufficient to eliminate the need for supplemental irrigation entirely, achieving two points.
As an example, the Twin Creeks Science and Education Center in Great Smoky Mountains National Park, which is targeting LEED Silver certification, was designed to maintain the existing natural forest plant palette, eliminating the need for supplemental irrigation, and qualifying for both Water-efficient Landscaping points.
When landscape design strategies alone are not sufficient to reach a project’s irrigation efficiency goals, the next step is meeting demands efficiently through optimization of the irrigation system design. Use of high-efficiency drip, micro and sub-surface systems can reduce the amount of water required to irrigate a given landscape. The U.S. Green Building Council reports that drip systems alone can reduce water use by 30 to 50 percent. Climate-based controls, such as moisture sensors with rain shut-offs and weather-based evapotranspiration controllers, can further reduce demands by allowing naturally occurring rainfall to meet a portion of irrigation needs.
Finally, greening the supply can be achieved by tapping alternate water sources. LEED recognizes two alternate water sources: rainwater collection and wastewater recovery. Rainwater collection involves collecting and holding on-site rainfall in cisterns, underground tanks or ponds during rainfall. This water can then be used by the irrigation system later during dry periods. Wastewater recovery can be achieved either on site or at the municipal scale.
On-site systems capture gray water (which does not contain human or food processing waste) from the building for irrigation use. The Biodesign Institute at Arizona State University, LEED-certified at the Platinum level, captures condensate from the mechanical system, storing it in an underground tank for irrigation use. (See project profile.)
The Gwinnett Environmental & Heritage Center in Buford, Ga., LEED-certified at the Gold Level, makes use of municipally supplied treated wastewater for irrigation. Non-potable water is supplied as needed via a municipal supply line from Gwinnett County’s wastewater treatment plant.
LEED points for the water-efficient landscaping credits can be earned most effectively with early planning. When incorporating rainwater collection or wastewater recovery in particular, it is crucial to assemble a team of experts and establish project roles early in the process. Rainwater collection and wastewater treatment systems span multiple conventional project disciplines, making it especially important to clearly articulate responsibilities. Water-efficient landscape and irrigation system design require an experienced landscape architect.
Local requirements for rainwater harvest and wastewater treatment vary greatly, so early involvement and input from local code officials is also important. If the facility executive assembles an experienced team, including the architect, landscape architect, civil and plumbing engineers and rainwater system designer, early in the design process, realistic efficiency goals can be set collaboratively and achieved cost effectively.
Innovative Wastewater Technologies
The intent of the Innovative Wastewater Technologies credit is to “reduce generation of wastewater and potable water demand, while increasing the local aquifer recharge.” One point is awarded for either reducing potable water use for sewage conveyance by 50 percent, or for treating 50 percent of wastewater on site to tertiary standards (with the treated water infiltrated or used on site). Tertiary treatment is the final stage of treatment before water can be discharged back into the environment.
In the case of wastewater, the first step in the usual water-use optimization process, reducing demand, is not applicable. Occupant requirements for trips to the restroom are a constant. Strategies for meeting the first compliance option, reducing potable water use for sewage conveyance, therefore fall into two categories that can be used either independently or in concert. By simply meeting demands efficiently, ultra high-efficiency plumbing fixtures can reduce the water required for sewage conveyance by more than the 50 percent requirement.
For instance, composting toilets and waterless urinals use no water. These two technologies alone can eliminate a facility’s use of potable water for sewage conveyance, qualifying both for this credit’s point, plus potentially a LEED Innovation in Design point for exemplary performance. It should be noted, however, that composting toilets are used rarely in commercial facilities.
Alternately, if the selected plumbing fixtures alone are not adequate to reach the 50 percent reduction threshold of the first option, or if ultra high-efficiency plumbing fixtures are not selected, the water necessary for toilet and urinal flushing can be reduced by a minimum of 50 percent, or eliminated entirely, through use of rainwater collection or wastewater treatment strategies.
The Southface Eco Office in Atlanta provides an example of how this credit can be achieved. The facility, targeting LEED Platinum certification, completely eliminates the use of potable water for sewage conveyance using a variety of complementary strategies. In the staff restrooms, foam flush composting toilets, which require only six ounces of water per use, plus waterless urinals, dramatically reduce the volume of water required for sewage conveyance. In the public restrooms, water requirements are reduced via a combination of dual-flush toilets, ultra-high-efficiency toilets and waterless urinals. The remaining water required for sewage conveyance — a greatly reduced volume — is supplied via rainwater collected from a roof-mounted solar array and stored in a rooftop cistern, plus a supplemental in-ground storage tank.
The second option for meeting this credit’s requirements is treatment of at least 50 percent of wastewater on site to tertiary standards. This can be achieved with biological remediation systems, such as “living machines,” which use natural biological activity to break down wastes, or via more conventional wastewater treatment systems, which would typically only be economically feasible on very large projects.
A capable team and early involvement of local code officials are critical components for the successful design and implementation of non-potable water supply systems. Some ultra-high-efficiency fixtures, such as composting toilets, also have unique spatial requirements. In addition, dual-plumbing lines for non-potable water supply within the building are fairly easy to plan for initially, but much more difficult to retrofit later.
Water Use Reduction
The intent of the Water Use Reduction credit is to “maximize water efficiency within buildings to reduce the burden on municipal water supply and wastewater systems.” One point is awarded for reducing water use by 20 percent, two points are awarded for reducing water use by 30 percent. The fixtures governed by this credit include water closets, urinals, lavatory faucets, showers, and kitchen or break room sinks. Other water-using fixtures and equipment, such as dishwashers, clothes washers and mechanical equipment, are not addressed by this credit; however, water efficiency measures for these “non-regulated” uses can qualify for a LEED Innovation in Design point.
Again, the first step in the optimization process, reducing demands, is not applicable. It’s not possible to design away occupants’ needs to use the restroom, wash their hands or shower. Strategies for water-use reduction therefore fall into the same two categories identified for Innovative Wastewater Technologies: either meeting demands efficiently or supplying the demand in alternate, more environmentally responsible ways. The two credits are complementary: Water savings related to the Innovative Waste Water Technology credit will also contribute to the Water Use Reduction credit.
In addition to the rainwater collection and wastewater treatment strategies, and the water-efficient plumbing fixtures (such as dual-flush toilets, waterless urinals and composting toilets), low-flow lavatory faucets and low-flow showerheads also contribute to meeting demands efficiently. For both credits, the baseline water use against which efficiency measures are evaluated is 1.6 gallon-per-flush toilets, 1 gallon-per-flush urinals, and 2.5 gallon-per-minute faucets and showers.
The 30 percent reduction necessary to earn both points for this credit is achievable with proven, cost-effective technologies. Simply using low-flow lavatory faucets with automatic controls (0.5 gallons-per-minute, 12 seconds per use) is typically sufficient to achieve a 20 percent reduction in water use, qualifying for one point. Waterless urinals typically achieve an additional 14 percent reduction which, when combined with low-flow faucets, typically exceed the 30 percent reduction threshold, thereby earning both points.
Dual-flush toilets and flushometers, which allow users to choose a standard 1.6 gallon flush for solid waste, or a lower 0.8 to 1.1 gallon flush for liquid, will typically yield more than a 10 percent reduction in water use. Another option is ultra low-flow toilets, which use less than 1.6 gallons per flush. These fixtures are now produced by many major fixture manufacturers. When combined with low-flow faucets and waterless urinals, dual-flush or ultra-low-flow toilets can achieve more than a 40 percent reduction in water use, qualifying for both Water Use Reduction points, plus an Innovation in Design point for exemplary performance. All of these strategies were employed at the Southface Eco Office, resulting in a project expected to use only one-quarter of the water of a conventional facility.
Among the three LEED Water Efficiency credits, Water Use Reduction can often be achieved without the early planning and design integration required by the other two credits. Most alternative plumbing fixtures use conventional plumbing supply and waste lines, allowing these fixtures to be substituted for less-efficient standard fixtures at any point in the design process, and even well into the construction process.
With freshwater projected to become increasingly scarce, water efficiency measures can extend this limited resource while reducing waste and decreasing operational costs. In spite of LEED’s limited emphasis on water efficiency, water-efficient design should be a goal of any project.
John Starr, AIA, is a principal with Lord, Aeck & Sargent. As a leader in the firm’s Science Studio and as director of the firm’s Arts & Culture Studio, he focuses on designing buildings that incorporate sustainability as a core part of their mission. Jim Nicolow, AIA, is a senior associate with Lord, Aeck & Sargent. He leads the firm’s Sustainability Initiative.