What steps can you take to maximize water efficiency in LEED projects that help reduce our planet’s carbon footprint?
So much has been talked about in the green building movement regarding the role of Leadership in Energy and Environmental Design (LEED) in promoting energy efficiency measures, but what about the important role that LEED can also play in water efficiency measures? There are many reports about substantial energy efficiency gains of over 30% to 40% when compared to standard energy codes occurring in LEED buildings due to smart lighting, HVAC, and daylight harvesting, to name a few. But, did you know on a percent basis, potable water use efficiency gains can be even more dramatic? This article highlights how water efficiency assists in LEED certification for building projects.
The challenge for the future’s growing infrastructure is to locate, secure, and maintain a clean and abundant water supply. A human can survive for weeks without food, but only 48 hours without water. Potable water supplies are becoming unsustainable in many urban areas that appear to be impacted by global and regional climate change. One way to preserve sustainable potable water supplies is to build sustainable buildings and infrastructure whose water savings performance can be evaluated and verified using a point-based rating system like LEED.
The LEED rating system was founded by the United States Green Building Council (USGBC) around 1993. The USGBC is a non-profit non-governmental organization based out of Washington D.C. The USGBC now has over 20,000 member organizations, which include eight regions with at least 70 local chapters organized and maintained by industry volunteers.
The LEED rating system is a consensus-based, market-driven building rating system that evaluates the environmental, energy, and water performance from a whole building life cycle approach. At present, there are five separate LEED rating systems that include both newly constructed and existing buildings. The rating systems include the following:
- LEED for New Construction (NC)—mainly for new construction or major renovations
- LEED for Core and Shell (CS)—mainly for speculative office buildings
- LEED for Commercial Interiors—tenant fit outs or tenant improvements
- LEED for Existing Buildings Operations and Maintenance—for efficiency measures conducted in occupied space
- LEED for Homes—completed in 2007 for high-performance homes
- LEED for Neighborhood Development, Retail, and Healthcare are all in pilot phase and ready to be implemented sometime in 2009.
LEED is organized into performance categories depending upon the rating system. For instance, LEED NC includes six performance categories such as Sustainable Sites (SS), Water Efficiency (WE), Energy & Atmosphere, Materials & Resources, Indoor Environmental Quality, and Innovation in Design (ID). Each category contains credits that may have one or more points. Some categories also have prerequisites that must be achieved in order to be eligible for LEED certification at any level. The rating system levels include the elementary level that is certified, followed by increasing point totals to achieve Silver, Gold, or Platinum. The total points eligible for each rating threshold depends upon the rating system.
LEED 2009 or Version 3 has been developed as an overhaul to the older LEED rating systems. Most of the rating systems are now based on a point total of 110 points. For instance, LEED 2009 will overhaul the LEED NC point distribution from 69 points to 110. Table 1 provides a cross-reference between the two rating system versions.
Table 2 contains a cross-reference table to the point threshold levels needed for LEED certification in the two LEED NC versions. LEED certification is a process that needs to be managed and protocols followed. This includes first registering the project with the USGBC with the intent that the project will be certified at a later date. Certification review occurs after the applicant submits documentation on all prerequisites and eligible credits reviewed by a third-party review body that is administered through the Green Building Certification Institute (GBCI), formed by the USGBC in 2008. The documentation is managed by completing online “Credit Templates” using a Web-driven process called “LEED Online.” The GBCI-accredited reviewer then reviews the clarity and completeness of documentation for each credit and prerequisite in order for the applicant to achieve certification.
Water and “Embedded Carbon”
Indoor and outdoor urban water contains “embedded energy” or kilowatt-hours of energy consumed per volume as water is extracted and/or pumped, treated, and possibly stored for later extraction and use. Indoor urban water also contains embedded energy resulting from collecting, treating, and discharging the wastewater generated from indoor activities. In most cases, this embedded energy intensity depends upon location of the water sources and end user. For instance, the California Energy Commission (CEC) conducted a number of studies related to the energy usage to manage potable water for urban uses in southern California that originates from northern California. Findings indicate that it takes 11,111 kWh of energy to extract, treat, store, and distribute a million gallons of southern California water that originates in northern California, as compared to 3.2 times less energy (3,500 kWh) for northern California to manage its own urban water (Refining Estimates of Water Related Energy Use in California, California Energy Commission [CEC], December 2006). Urban water that is used indoor also uses an additional 1,911 kWh to treat the wastewater generated by this use that does not occur with outdoor water use.
Table 3 summarizes the differences between embedded energy and associated greenhouse gas (GHG) emissions in northern and southern California urban water. Carbon dioxide equivalent (CO2e) emissions resulting from this urban water use can be estimated using electricity emission factors from US Environmental Protection Agency (USEPA) eGRID2007 Version 1.1, and carbon equivalent methane (CH4) and nitrous oxide (N2O) emissions estimated from typical domestic wastewater treatment processes in the EPA’s annual US Greenhouse Gas Emissions Inventory. The total 2007 US wastewater CH4 and N2O emissions was estimated by the EPA to be 20.7 million metric tons CO2e, which equates to 0.4176 pounds of CO2e emissions per capita per day attributed to CH4 and N2O emissions. Southern California and northern California GHG emissions intensity factors can now be estimated from the above assumptions to be 0.01095 pounds CO2e per gallon of water imported to southern California and 0.00542 CO2e per gallon of water for northern California (see Table 3). Please note that the majority of the emissions in the northern California indoor water case (about 53%) are attributed to CO2-equivalent emissions of CH4 and N2O in wastewater treatment. This example illustrates that the CH4 and N2O emissions from wastewater treatment cannot be ignored as a major emissions source in any urban water supply used for indoor purposes. 
The next valuable exercise is to estimate typical carbon emissions per capita per day by multiplying the total urban water emissions per gallon by the urban water consumption in gallons per capita per day (GPCD) that is identified as a baseline year 2005 statewide estimate of 192 gallons GPCD in California’s 20x2020 Water Conservation Plan Draft, State Water Resources Control Board (SWRCB), April 30, 2009. Typical total urban water emissions per capita per day are estimated to be of 1.04 pounds CO2e for northern California and of 2.10 pounds CO2e for southern California (see Table 3).
Consequently for southern California water users, the energy and associated GHG savings for each 1,000 gallons of imported water saved in southern California for indoor urban use equates to approximate savings of 13 kWh of electricity and avoidance of 13.8 pounds of CO2e GHG emissions. For example, a typical waterless urinal in southern California that saves 40,000 gallons of indoor urban water each year could also save 520 kWh of energy and 552 pounds of CO2-equivalent GHG emissions.
The above example is an idealized estimate of the differences in urban water embedded carbon. More studies are sorely needed to estimate the carbon emission intensity factors for all significant urban water supplies, because every supply will have its own unique embedded carbon intensity factor. This includes not only considering carbon emissions from indirect electricity consumption, but also the emissions that can be attributed to CH4/N2O emissions from wastewater treatment.
Lastly, this embedded carbon intensity does not include the energy consumed during pumping and heating of water for consumer end use. This energy has been estimated to be at least 50% of the total embedded energy in urban potable water according to Refining Estimates of Water Related Energy Use in California, CEC, December 2006.
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Photo: Crown Communications
Meanwhile, in Charlotte, NC, the Sanctuary—built by Crescent Communities in Raleigh, NC—features 187 homes on 1,300 acres bordering Lake Wylie in
Charlotte. The Sanctuary’s lodge was the first recreational facility in North Carolina to be certified by the USGBC’s LEED. |
LEED Water Credits
There are at least 12 points that can be influenced by water efficiency in LEED 2009, including potentially an additional three points for innovative or regional credits. Below is a discussion of these indoor, outdoor, and innovative water efficiency measures that help towards LEED certification achievement.
How to Achieve 40% Indoor Savings
The newest LEED 2009 rating systems have made it a prerequisite that the indoor water savings in LEED-certified buildings for commercial, industrial, and high-rise multifamily residential to be at least 20% better than the maximum baseline flush volume and flow rates established by the Energy Policy Act (EPAct) of 1992 for water closets, urinals, lavatory faucets, shower heads, and kitchen faucets. WE c3 for instance, can achieve up to three points if water savings of 30%, 35%, and 40% savings are verified. This 20%-savings prerequisite benchmark can be easily achieved if the project is a non-residential project, because these projects typically implement “pint flush” or waterless urinals exhibiting over 90% water savings when compared to the baseline flush volume of 1.0 gallon per flush (gpf) EPAct maximum flow rate for urinals. Conversely, high-rise multifamily residential projects struggle sometimes to achieve at least a 20% water savings, because they implement no urinals, and showers are used much more frequently than in commercial projects.
Table 4 summarizes three LEED projects and their relative water use. These three southern California projects were selected in order to compare three different building types that had similar building code and climate. The total usage in gallons was calculated using the WE 3 LEED-OnLine Template calculator. (Please note: The calculator only totals up total quantity and not individual fixture quantities.) One is a LEED-CS Class A speculative office with four stories in San Diego County, CA, the second a LEED-NC 23-story, high-rise apartment tower in San Diego County, and the third a LEED-NC Gold-certified, state-of-the-art student worship center at in Lake Forest, CA. The office tower and worship center both achieve over 40% potable water savings and three LEED points, versus the high-rise apartment tower that barely achieved the 20% water savings LEED 2009 prerequisite. The relatively greater unit consumption of potable water for the residents (26.1 gallons per day [gpd]) compared to office occupants (4.7 gpd) is mostly related to each resident taking a shower each day, and using water closets and faucets 67% more than the office occupants.
One challenge to the LEED template water calculator is evident in the results of the Student Worship Center. It appears that the indoor efficient fixtures are saving almost 50% potable water, but on an annual basis it is only 67,000 gallons of savings for such a busy place of assembly. What causes this situation in projects that have a low full-time equivalents count but a high visitor count? The LEED template calculator only assumes that up to a half of those visitors will use the restroom while they are there visiting the building. This, of course, skews the result to a smaller water savings and associated GHG emission savings in those building cases.
Another shortcoming of the LEED water calculator is considering potable water savings related to process water, laundry, and other water processes that may occur in new buildings but are not of the EPAct list of water fixtures. These water saving strategies can be claimed as an ID credit that can be submitted to the GBCI for review and approval.
Outdoor Water Credits
The outdoor water credits are focused on reducing or eliminating the use of potable water being used for irrigation of landscaping. Reducing or eliminating the usage of outdoor potable water will save substantial resources. As mentioned previously, it is generally assumed that outdoor water consumption is about half of the total urban water usage in most California regions.
WE c1.1 requires reduction of potable irrigation water use of 50% versus a baseline case potable irrigation water demand in the month of July when evapotranspiration rates are typically greatest. This credit is typically easily achieved if drought-resistant native or adapted plant species are utilized in concert with high-efficiency irrigation elements and control technology. The second credit WE c1.2 is less easily achieved, because potable water irrigation must be eliminated utilizing one or a combination of captured rainwater, graywater, onsite tertiary-treated wastewater, or offsite reclaimed wastewater to irrigate the landscape. Another WE c1.2 option is to implement landscaping that needs no supplemental irrigation after a one-year plant propagation period.
Calculation of WE c1.1 achievement is completed typically by the Landscape Architect estimating total potable water applied during the month of July using commonly known evapotranspiration constants and plant species factors of plant coverage, transpiration, and water uptake for both the baseline and design cases. The baseline case typically uses higher water consuming vegetation (turfgrass, etc.) with less-efficient irrigation methods (sprinklers) in order to calculate the baseline water application. The design case contains a more water efficient plant palette, arrangement, and irrigation methods in order to achieve a minimum 50% potable water savings. Additionally, the design case water use can be minimized if non-potable water from rainwater, graywater, condensate water, or treated wastewater sources is incorporated as an irrigation source. Typically, the assumptions used in the calculations can be subjective based on the Landscape Architect’s experience and knowledge of project-specific plant and irrigation factors.
The student worship center in Lake Forest, CA, utilized substantial native or adapted landscaping of approximately 50,000 square feet (sf) on a site area of about 160,000 sf including a 2,300-sf intensive green roof, and 12,500-sf drought-resistant turfgrass. This project achieved both WE c1.1 and 1.2, because all of the water used for irrigation is non-potable tertiary treated wastewater from the local water authority Irvine Ranch Water District. Even though the project is using non-potable irrigation water, the total potable water applied in the design case still needs to be at least a 50% less than the potable water applied estimated in the baseline case to achieve WE c1.1. The design was able to realize almost 20,000 gallons of total potable urban outdoor water, or a 50.6% savings when compared to the baseline case, which translates into avoiding GHG emissions of 162 pounds CO2e. The actual savings of GHG emissions for this case using locally reclaimed wastewater is much less than imported potable water. In some cases, reclaimed wastewater used for irrigation may contain 10% of embedded GHG emissions of a comparable imported potable water supply because locally reclaimed wastewater typically contains a much lower embedded energy intensity (California’s Water-Energy Relationship Final Staff Report, November, 2005, CEC).
Technology Coming to a Project Near You
Technologies for saving potable water are becoming more prevalent as water supplies diminish and code officials open up to newer water-saving ideas. For LEED projects these technology options can help achieve a number of LEED credits in the SS, WE, ID, and newly developed Regional Priority Credits.
Rainwater harvesting for flushing toilets or irrigating landscape can contribute up to three LEED credits (WE 1.2, WE 2, and ID). This process utilizes above or below grade rainwater retention (“cisterns”) plus filters, pumps, and vector control (if needed) to retain and reuse collected rainwater. For every inch of rainfall that collects on a 1,000 sf surface, up to 623 gallons of rainwater can be collected, stored, and reused.
There are commercially available rainwater harvesting, storage, and filtering systems available on the market now, and www.harvesth2o.com has comprehensive information about rainwater harvesting.
Graywater recovery for flushing toilets or irrigating landscape can contribute up to three LEED credits (WE 1.2, WE 2, and ID). This process utilizes water from lavatories, showers, drinking fountains, and washing machines to be treated/filtered and reused for flushing toilets, irrigation, or, in some cases, just infiltrated into the soil. This approach is becoming increasingly popular in areas when local jurisdictions have codes for graywater reuse. The graywater system must include plumbing modifications to ensure that it will work properly, and a storage or surge tank/filtration system must also be implemented.
Graywater recovery on commercial projects can be typically economically viable for irrigation reuse assuming the initial plumbing cost premium is feasible, and shower water is available for collection and reuse. There are at least six commercially available graywater reuse systems available for the market with many more being commercialized. Oasis Design has extensive resources about graywater on its Web site www.oasisdesign.net, and www.greywater.com is another viable resource.
Green roofs for stormwater retention and primary treatment. Green roofs can contribute to achieving at least eight LEED credits in LEED 2009, and is seen as one of the ways for projects to achieve LEED Gold- or Platinum-rating thresholds. Green roofs are constructed on top of structurally sound roof decks and plaza decks typically overlying occupied space. Green roof assemblies consist of a properly installed and inspected roofing membrane assembly (likely includes insulation), drainage media, growing media (soil, compost, mineral media, among others), and planting media. The different medias can be installed loose laid or via modular trays. Typically, most green roofs are installed on flat roofs; however, Europe has had great success installing green roofs on slopes exceeding 10%.
Green roofs are considered “extensive” if the growing media is thinner than 6 inches, intensive if the growing media is thicker than 6 inches, or semi-intensive (containing both thin and thick areas). Different performance objectives in stormwater retention/use, structural support, and insulation values can be experienced and need to be designed into the system using best available design practices.
Fully installed costs of green roofs range from $15 to $50 per sf, depending upon the roof area, type of green roof, level of access to the roof, and type of landscaping and corresponding irrigation system, if any. Two Web sites that provide extensive resources include Green Roofs for Healthy Cities www.greenroofs.org and Greenroofs.com at www.greenroofs.com.
Onsite tertiary treatment and reuse of “black water” can contribute up to three LEED credits (WE 1.2, WE 2, and ID). This integrated whole building wastewater treatment system is not typically used except on relatively large projects where volume of wastewater can justify the initial cost of the system. These systems typically include a packaged solids handling, bioreactor, tertiary polishing system with final filtration, and disinfection. More information regarding these systems can be located within the US EPA’s Onsite Wastewater Treatment Systems Manual, EPA/625/R-00/008 February 2002.
USGBC has also developed a catalog of innovative design options that have been approved for an ID credit, such as process water savings, wastewater savings, and other water-related innovative design options successfully implemented in LEED-eligible projects. Go to www.usgbc.org and link to the LEED ID Credit Catalog for more information.
Innovative Case Studies
Summarized below are two LEED NC
projects that successfully implemented innovative water efficiency measures to maximize LEED certification.
Tempe Transportation Center, Tempe, AZ. The 40,000-sf City of Tempe transportation center construction was completed in the summer of 2008 as a bus and light rail intermodal hub, office, and retail complex. It is a LEED Platinum-pending facility that contains the following innovative water efficiency measures:
- Separate graywater system that recycles graywater from showers, sinks, and drinking fountains to refill water closets (helps achieve WE 2 credit for innovative wastewater technology)
- A rainwater harvesting system that includes a 12,000-gallon subterranean cistern that stores rainwater that is then used for drip-irrigating landscape, and water for power-washing public plaza areas (helps achieve WE credits 1.1 and 1.2). The owner was only able to provide a fraction of rainwater storage that the project is designed for (600,000 gallons subterranean short-term stormwater storage) because of jurisdictional water quality and mosquito abatement ordinances.
- A green roof that includes specially designed and pilot-tested drought-resistant Sonoran desert landscape. The LEED credits this green roof may contribute to the project include open space (SS c5.2), stormwater quantity and quality (SS c6.1/6.2), and heat island roof and non-roof mitigation (SS c7.1/7.2). The green roof will also provide energy savings and noise reduction benefits because of the insulating and sound-dampening abilities of a green roof.
- Dual-flush toilets and water-free urinals were used to achieve over 40% potable water savings indoors (achieves WE 3.1/3.2 and ID credit).
The information for this case summary can be found in an article by Scott Blair in the June 2007 Southwest Contractor, and an article by William Hermann in the November 4, 2008 The Arizona Republic, titled “Tempe building to be supergreen.” Additional information on the project can be found at www.tempe.gov/greenprograms/transitcenter.htm.
The Solaire, New York City, NY. The Solaire is a 357,000-sf multifamily luxury complex located at 20 River Terrace in Battery Park, New York City. This LEED-NC Gold project was completed in August 2003 and has been awarded many distinctions because of its sustainable design, water and energy efficiency measures, and measurement and verification systems. The Solaire contains the following innovative water efficiency measures:
- Intensive rooftop gardens on the 17th and 27th floors retain and filter up to 25,000 gallons of runoff/stormwater each day. Stormwater not retained in the gardens is drained into a 10,000-gallon storage tank when it is filtered and then reused back up on the rooftop gardens for irrigation. These rooftop gardens contributed to among others, achievement of LEED credits SS c6.1/6.2, SS c7.1/7.2.
- A wastewater treatment system that treats 25,000 gallons of “black water” each day to tertiary treatment standards. This specially designed and operated treatment system includes a bioreactor, filter, and oxidation/disinfection and reverse osmosis polishing before the tertiary treated wastewater is used to fill water closets, provide cooling tower makeup water, and irrigate adjacent ground level gardens. This innovative wastewater system helped achieve at least WE 2 and one ID credit for LEED Gold achievement.
- Water efficiency measures were utilized inside the building to reduce the potable water use by specifying water efficient water closets, clothes, and dishwashing machines. The plumbing fixtures used for the building were designed to save at least 50% potable water compared to maximum EPAct 1992 plumbing fixtures, so that WE c3.1/3.2 and ID credits were achieved.
Overall, the water/wastewater systems have been performing as expected and total water use for 2007 was measured to be 52,618 gpd, or 75 GPCD for residents, which included 37% of that reused water from the innovative wastewater system. The total water use was measured to be 0.15 gpd per sf of building area. Additionally, no potable water is utilized to water the rooftop gardens and adjacent ground floor landscape, so WE c1.2 was also achieved.
Information for this case study was taken from “NYC’s Living Lesson” by Kyra Epstein in High Performing Buildings, summer 2008 edition, and through a link to the project via www.urbangreencouncil.org/resources/green-buildings/the-solaire.html.
Better Jump on the LEED Bandwagon Now
The process of LEED certification is becoming increasingly important in designing and constructing robust and sustainable buildings whose performance can be measured and verified. It is doubly important to the water/wastewater industry that their products, systems, construction, and operations contribute to the LEED evolution as McGraw Hill estimates in its 2006 Green Building SmartMarket Report, that in 2010 approximately 10% of all new commercial construction building starts are expected to be green buildings.
The best management design, construction, and operations practices incorporated by the LEED Rating System can incrementally help save precious potable water resources that feed the built environment. For instance, a recent study titled Green Building Impact Report 2008 by Rob Watson and Elizabeth Balkan, with Greener World Media, estimates that in 2008 over 9.5 billion cumulative gallons of potable water has been saved by LEED-certified buildings since the inception of LEED in the 1990’s. This would equate to avoided GHG emissions of approximately 23,356 Metric Tons of CO2e when applying the northern California urban water carbon intensity factor of 0.00542 pounds CO2e per gallon of urban water. Watson and Balkan also estimate that this savings will increase at least an order of magnitude to 133.4 billion gallons of water by 2015, because of the future growth of LEED-certified buildings.