While significant progress in water conservation has been made inside buildings—primarily with the widespread adoption of high-efficiency plumbing fixtures—much of the water consumption in buildings actually occurs outside the structure itself. In a typical hospital or office building, for instance, landscape irrigation and cooling tower makeup water can account for more than half o...
While significant progress in water conservation has been made inside buildings—primarily with the widespread adoption of high-efficiency plumbing fixtures—much of the water consumption in buildings actually occurs outside the structure itself. In a typical hospital or office building, for instance, landscape irrigation and cooling tower makeup water can account for more than half of total water consumption.¹ In warm regions like the Southeast, cooling towers alone can consume more than half of total water use in large buildings.² Schools, college and university campuses, museums, suburban office complexes, stadiums, and single-family homes can often use massive amounts of water for irrigation to maintain green space.
In recent years, the building community has made great strides in improving water performance outside buildings. Some measures, like stormwater management planning and installation of retention ponds, are mandated by local codes or permit requirements. Other approaches, such as water-efficient irrigation systems and low-water-use landscaping, are gaining popularity because of relatively short payback periods and contribution toward green building certification.
Building Teams are implementing a broad range of exterior water-efficiency measures to achieve water reduction goals, according to the 2009 BD+C/Professional Builder 2009 White Paper Survey. Survey respondents that work on nonresidential building projects said they have implemented 6-7 exterior water-efficiency technologies or systems on projects in the last 18-24 months. Moreover, respondents said they expect to use 9-10 measures within the next two years (Table 4.2). Among the most popular measures are stormwater management plans, retention ponds, low-water-use landscaping/indigenous planting, drip irrigation systems, and pervious pavement.
Similarly, nearly half of our Residential Survey respondents (48%) said they're already using drip irrigation, and 40% said their companies are using automated irrigation systems. Many more are already employing stormwater management plans (73%) and retention ponds (55%) (Table 4.2).
Applying one or more of these design practices and technologies can save building owners thousands and even millions of gallons of water annually. Take the LEED Platinum One Bryant Park tower in New York City for example. Stormwater harvesting and cooling tower condensate recovery alone are saving an estimated 5.8 million gallons of water a year, resulting in net annual savings of $12,750 on water costs.³
Landscape irrigation represents a significant portion of overall water use in both residential and commercial buildings. In Phoenix, for example, irrigation accounts for about two-thirds of total residential water use, and even in water-rich areas like Seattle and Tampa, irrigation represents more than a third of total household water use.4
“Landscape irrigation can be as much as 60% of water use in homes, especially in arid climates,” says Jennifer Riley-Chetwynd, with Rain Bird, Azusa, Calif., a manufacturer of residential and commercial irrigation systems. “Even in commercial settings, you should be asking how well you are managing your water use.”
Newer technologies are helping building owners reduce water use for landscape irrigation functions. One particularly promising technology is weather-based irrigation. Instead of watering according to a preset schedule, these “smart” systems take into account prevailing weather conditions, current and historic evapotranspiration, and soil moisture levels to provide the ideal amount of water based on the needs of the plants. By watering based on need, property owners have been able to achieve immediate water usage reductions of 5-7%, according to a four-year study of 2,294 smart controller installations across California.5
The study found that 53% of locations were over-irrigating their property before installation of the smart controllers, based on a theoretical irrigation requirement (TIR) for each property. Forty-seven percent of locations were at or under the TIR threshold; in fact, according to Peter Mayer, a consultant with Aquacraft Inc., a good portion of these properties were actually using too little water on their grounds. (This resulted in an average increase in water use of 1.49 kgal, or 0.43%, for those locations. But as Fiona Sanchez, conservation director for the Irvine Ranch [Calif.] Water District, noted at the October 2009 WaterSmart Innovations Conference in Las Vegas, “If smart controllers deliver to the theoretical requirement, that's what the controllers were supposed to do.” In other words, the controllers did their job.)
The study concluded that while weather-based controllers are an important piece of the puzzle, they're not the single solution for achieving perfect irrigation control and water savings. “Even the best, most water-efficient controller cannot make up for poor system design, installation, and maintenance,” the authors stated.
The authors stress the need for a holistic approach to irrigation and landscape design. Given the complexity of site design, landscape architects and related professionals deserve a seat at the design table on projects—a rare occurrence even for the most fully integrated Building Team. Speaking at the WaterSmart Innovation conference, Kerry Blind, FASLA, LEED AP, president of Ecos Environmental Design, Atlanta, said that landscape architects can bring sustainable design practices involving the use of techniques like bioswales, rainwater harvesting, vegetated roofs, porous pavement, ideal plant life selection, and retention ponds to improve water management.
The bulk of building projects in the U.S. miss out on one of the most potentially significant water conservation opportunities by failing to consider one key tool: rainwater catchment and reuse.
Consider these facts: For every inch of rain that falls on a thousand square feet of roof area, 600 gallons of water can be collected for harvesting. In central Texas, a home or commercial building that size could expect to collect upwards of 20,000 gallons a year.6 In rain-heavy regions like the Northwest and Southeast, the same-sized structure could collect up to five times that amount annually. The numbers are staggering when extrapolated over large areas or regions. For instance, if just 10% of the roof area in Texas were used for rainwater harvesting, an estimated 38 billion gallons of water would be conserved each year—water that would otherwise run off site, taxing storm sewer systems and contributing to erosion.
Compared with graywater reuse systems, rainwater harvesting is relatively simple to execute, especially for irrigation and cooling tower makeup applications, which don't require costly, complicated dual piping systems and oftentimes call for only minimal water treatment. Moreover, the emergence of “packaged” rainwater harvesting systems is making it easier for building owners and even homeowners to implement the technology (see sidebar).
“This is such a simple and obvious thing to do in much of the country that one wonders why it has taken so long to be considered as a viable new water supply,” said green building consultant Jerry Yudelson, PE, LEED AP, in his recent report on water-efficiency technologies for the Mechanical Contracting Education and Research Foundation.² “In addition to providing onsite water supply and reducing the need to use potable water for lower-quality water uses, rainwater harvesting can help reduce stormwater runoff from building sites.”
Yet, despite the huge potential for water savings, rainwater reuse is still relatively rare in U.S. building projects. Only about a third (34%) of AEC respondents to the 2009 White Paper Survey said they specified rainwater harvesting or retention systems for outdoor use in nonresidential projects in the past 18-24 months. Even fewer residential building respondents (26%) said their companies had implemented such systems within the past two years.
In some areas of the country, like parts of Utah and Washington and, until recently, the entire state of Colorado, rainwater collection is restricted—and even illegal—without special permits from the local authorities. Opponents of rainwater harvesting see it as a water rights issue: If too many building owners adopt the practice, it will greatly reduce water flow to streams and aquifers where it is needed for wells and springs. They see this as being akin to stealing water from downstream users who are legally entitled to the water.7
By contrast, states and jurisdictions in water-scarce regions like the Southwest are offering incentives for the installation of rainwater collection systems. Texas offers rebates of up to $40,000 for building owners that install collection and reuse systems. Santa Fe County, N.M., and Tucson, Ariz., actually require these systems on certain new building projects.7
“Rainwater collection for irrigation or even fixture flushing is something that we could use on almost every one of our projects,” says Dave Plasschaert, a mechanical designer with KJWW Engineering Consultants, Rock Island, Ill. “But cost and upkeep of this type of system are typically why it does not remain in projects very long.”
First cost remains a major concern with budget-conscious building owners. System costs can range from $20,000 to more than $50,000, with payback periods of a few years to well over a decade. In addition, because rainfall can vary greatly season to season, a supplemental potable water supply is typically required to meet supply demands, adding to both initial and ongoing costs.
However, in cases where buildings are designed to achieve 100% rainwater collection, the payback for collection and treatment systems can be almost immediate by eliminating costs associated with storm-drain hookups and related infrastructure and fees. This was the case at a California university project, where the cost to install two 20,000-gallon storage tanks and related collection, treatment, and distribution systems was less than the cost of tapping into the town's storm drains.²
Another issue impeding the adoption of rainwater harvesting is the lack of standards and regulations governing the design, installation, and maintenance of these systems, and allowed uses for the reclaimed water. This leaves local code officials and jurisdictions to interpret system design based on the current code, which can delay projects and result in higher first costs. For instance, some jurisdictions treat rainwater as graywater, limiting applications for reuse and requiring more-stringent treatment and storage measures. “That's where rainwater harvesting can get expensive because graywater oftentimes has special requirements,” says David C. Smith, PE, LEED AP, manager of plumbing and fire protection with Bala Consulting Engineers, King of Prussia, Pa.
Georgia, Texas, and Virginia are among a handful of states and cities that have published guidelines for the implementation of rainwater catchment systems. This past August, the American Rainwater Catchment Systems Association published a revised draft of its Rainwater Catchment Design and Installation Standards, which were developed in a joint effort with the American Society of Plumbing Engineers to be a national standards document. Next February, the International Association of Plumbing and Mechanical Officials (in cooperation with the International Code Council) will issue its Green Plumbing and Mechanical Code Supplement that introduces language that plumbing and building code officials can use to allow for rainwater harvesting in their jurisdictions. The hope is that these authoritative documents will help speed the code review and approval process for rainwater harvesting systems.
The growing demand for rainwater harvesting is spurring interest in siphonic roof drainage technology, which utilizes the principle of negative pressure to help draw water along horizontal piping and into the vertical drain. Unlike traditional gravity-based systems, which require multiple downpipes and ideal surface pitch to transport water off a roof, siphonic systems typically require just a few downpipes, reducing first costs and aiding in rainwater collection for reuse.
“We advise our clients to consider siphonic roof drainage for any roof project larger than 40,000 square feet,” says Randy Pool, PE, LEED AP, managing principal with architecture/engineering firm Stantec, Edmonton, Alb. At this threshold, says Pool, siphonic systems typically cost no more than traditional drainage approaches.
Cooling towers for chillers often are the largest consumers of water in buildings. Because these systems rely on water evaporation as part of the air conditioning process, they churn through thousands of gallons of water every minute. Considering that the average cooling tower uses three gallons of water per minute for every ton of cooling, a large commercial building with 1,000 tons of refrigeration will use 3,000 gallons of water per minute—10 times the amount of water used in the average household each day.²
Despite being water hogs, cooling towers are the predominant air cooling technology in the commercial building sector because of the significant energy savings they offer over alternative approaches. Newer “dry” cooling technologies like variable refrigeration volume systems show promise for reducing both water and energy use, but first cost is an obstacle to adoption of these systems.²
One obvious way to reduce cooling tower water use is to slim down the size of the cooling system through energy-efficient building design. By tightening the building envelope and implementing energy-efficient technologies like lighting controls, Building Teams can reduce overall cooling load required for a building, allowing for the mechanical systems like cooling towers to be downsized. Taking just 10 tons of required refrigeration out of a building can cut water use by 43,200 gallons a day.
Use of cooling tower water management techniques, such as conductivity meters and automatic controls, is another approach to conserving water. This is especially true with regard to blowdown, the process whereby water is removed from the system to reduce mineral concentration and scaling that occurs as a result of the evaporation process. Through real-time tracking and adjusting of blowdown water bleed rates based on evaporation rates, makeup water consumption can be reduced by 20% or more.6
Some progressive jurisdictions have instituted strict rules related to blowdown water usage. As part of its recently enacted water conservation ordinance, which goes into effect 1 December 2009, Los Angeles will mandate that cooling towers operate at a minimum of 5.5 cycles of concentration for blowdown use. The ordinance also outlaws use of single-pass cooling towers—systems that use 100% fresh water as the cooling medium—for air conditioning.8
Water treatment technologies, such as the Dolphin WaterCare system, help building owners achieve greater recirculation rates before requiring a blowdown to occur, according to John P. Cole, PE, LEED AP, a principal and assistant director of mechanical engineering with Albert Kahn Associates, Detroit. “The newer technologies are chemical-free and can greatly reduce water makeup requirements.”
Another potential opportunity for whole building water savings is the reuse of wastewater—including both blowdown and condensate—from cooling towers and other mechanical equipment for irrigation, and, in some cases, cooling tower makeup water and flushing water. Likewise, harvested rainwater and municipal-supplied reclaimed wastewater (so-called “purple pipe” water) can be used as makeup water for cooling tower equipment, reducing reliance on potable water (Table 4.1).
USGBC's LEED-EBOM program stresses these water reuse approaches by offering up to two Water Efficiency credits for supplying at least 95% of cooling tower makeup water from reclaimed sources, as well as an additional possible credit for cooling tower water management.²
To date, however, condensate recovery has not caught on all that well with commercial, institutional, and industrial design and construction firms. For instance, just 27% of AEC respondents to the 2009 White Paper Nonresidential Survey said that their firms had specified cooling tower condensate recovery systems in the past 18-24 months. And while 40% said they plan to specify cooling tower condensate recovery in the next couple of years, the adoption rate seems low considering the significant potential of this technology.
|Source||Definition||Typical uses||Requirements||Pluses and minuses|
|Source: Environmental Building News, 1 May 2008|
|Graywater||Wastewater collected in buildings from showers, bathtubs, clothes washers, and lavatory faucets||Nonpotable: usually used for subsurface irrigation||Separate wastewater drainage lines for graywater and blackwater, a filtration system, and usually storage; sometimes fed directly into subsurface irrigation piping||+ Reduces freshwater demand + Water volumes can be large + Emergency irrigation source – Difficulties with permits – Cost of dual piping – Risk of smell, O+M issues|
|Rooftop rainwater harvesting||Rainfall collected from a roof surface||Nonpotable: toilet flushing, irrigation, makeup water for cooling equipment; potable if adequately treated||A gutter system to channel rainwater into a cistern; often first-flush and filtration systems; treatment for potable uses.||+ Reduces freshwater demand + Rainwater is generally softer than well water + Avoided energy for pumping (if gravity-fed from a cistern) - Rainwater volume can vary|
|Landscape-scale stormwater harvesting||Stormwater collected on parking areas or other low-permeability landscape surfaces and stored in retention ponds||Nonpotable: toilet flushing, makeup water for cooling equipment||Topography that channels stormwater into retention ponds and a mechanism for withdrawal and use||+ Reduces freshwater demand + Fairly low cost – Difficult to manage stored water due to evaporation, vegetation|
|Air-conditioner condensate||Condensate captured from the evaporator coils of AC equipment or dehumidifiers||Nonpotable: toilet flushing, irrigation, makeup water for cooling equipment||Drainage of condensate lines into storage for reuse; only feasible in areas with adequate indoor humidity levels||+ Reduces freshwater demand + As distilled water, condensate is initially very pure + Water volumes can be large - Potential for contamination of stored condensate and lines|
|Mechanical equipment blowdown||Water bled from cooling towers and other mechanical equipment||Nonpotable: irrigation||Collection and storage components integrated with cooling towers and other sources of blowdown||+ Reduces freshwater demand + Water volumes can be large – Most blowdown water has high mineral content or other contaminants|
|Treat wastewater (building-scale)||Onsite treated wastewater (graywater or blackwater), producing nonpotable water||Nonpotable: toilet flushing, irrigation, makeup water for cooling equipment||On-site treatment system employing biological action, microfiltration, and sometimes reverse osmosis, UV, or chemical purification||+ Reduces freshwater demand - High installation cost - Sludge disposal remains - Can be energy-intensive|
|Treat wastewater (municipal-supplied)||Outflow from a sewage treatment plant after tertiary treatment and purification; distributed from water utility through separate piping (purple pipe)||Nonpotable: toilet flushing, irrigation, makeup water for cooling equipment||Separate supply plumbing for potable and nonpotable water; some water utilities provide such piping, most commonly tied to dedicated irrigation systems||+ Reduces freshwater demand + Energy savings compared with potable water use – Perception that treated wastewater is unsanitary|
|Desalinated water||Freshwater produced by removing salts from seawater or brackish water||Potable||Most desalination plants use reverse osmosis, forcing salt water through a specialized membrane that excludes salts||+ Reduces freshwater demand + Virtually unlimited supply – Energy-intensive|
|Used in last 18-24 months||Expect to use in next 18-24 months||Used in last 18-24 months||Expect to use in next 18-24 months|
|Source: BD+C/Professional Builder 2009 White Paper Survey
Respondents to the Nonresidential Survey used 6-7 “exterior” technologies or systems in the last two years (mean: 6.85) and expect to use 9-10 in the next 18-24 months (mean: 9.64), an indication of fairly widespread acceptance of water-efficiency techniques for dealing with stormwater and runoff problems and landscape irrigation. Among respondents to both surveys, stormwater management plans (Nonresidential, 71%; Residential, 73%) and retention ponds (Nonresidential, 64%; Residential, 55%) scored highest; these are often mandated by local codes or permit requirements. Planting low-impact vegetation and using more-efficient landscape irrigation systems also did well with both groups.
|Stormwater management plans||71%||77%||73%||77%|
|Low-water-use landscaping, indigenous planting||55%||70%||45%||60%|
|Drip irrigation systems||48%||59%||48%||55%|
|Pervious pavement (parking, walkways, etc.)||45%||68%||40%||56%|
|Automated irrigation systems (including evapotranspiration sensors, soil moisture sensors, weather-based systems, etc.)||42%||54%||40%||55%|
|Pressure-reducing valves (for landscape irrigation)||41%||54%||36%||45%|
|High-efficiency irrigation systems||37%||54%||30%||49%|
|Rainwater harvesting/retention systems (for outdoor use, e.g., landscape irrigation)||34%||59%||26%||45%|
|Green (vegetated) roofs||30%||54%||11%||20%|
|Turf reduction programs||28%||43%||22%||37%|
|Cooling tower condensate recovery systems||27%||40%||-||-|
|Low-impact development (“LID”)||27%||46%||23%||31%|
|On-site wastewater treatment systems||22%||32%||22%||26%|
|Rainwater reuse systems (for indoor use, e.g., flushing toilets)||17%||38%||5%||20%|
|Municipally provided recycled water systems (“purple pipe”)||13%||24%||8%||19%|
|Base: Nonresidential, 557; Residential, 131-132|