Efficient building water use

The escalating cost of providing potable water in the United States is creating new urgency for owners of commercial, industrial, and institutional buildings to respond with greater engineered water efficiency.


Learning objectives

  1. Understand the true cost of water in the commercial building sector.
  2. Learn about ways to conserve and/or reuse water.
  3. Learn about water standards and how they are changing. 

National surveys of the cost of public water supply utility rates show average annual rates of increase over the past 10 to 20 years as high as 8% per annum. According to an often-quoted survey of 100 U.S. cities whose findings were published in USA Today, rates of water/sewer utility cost increases from 2000 to 2012 average 7% per annum over that term with the greatest increases concentrated in the nation’s largest cities. 


This article has been peer reviewed

Proven techniques and technologies exist to design and retrofit for significant cost-justified water efficiency. Driven in part by the sustainable design movement, some strategies outpace existing regulations and codes. However, economic necessities, mainstreaming sustainable sensibilities, and the results of pilot testing of water reuse and recycling are combining to suggest that standards will soon catch up.

The rising cost of water

While other utility rates have generally tracked the Consumer Price Index, water and sewer costs have, in the past 30 years, increased at a much faster pace (see Figure 2). A web of interconnected reasons for the growth in water and sewer utility rates explains this phenomenon and suggests that the trend will continue (see sidebar, “Why is the cost of water rising?”). From the perspective of water’s status as a public good, some who monitor this issue suggest that the public has, perhaps reluctantly, accepted this cost phenomenon. Association of Metropolitan Water Agencies executive director Diane VanDe Hei sees it a bit differently. Observing Seattle’s 2011 move to increase water rates by 25% over a 3-year period, she suggests that despite a depressed economy and significant anti-tax sentiment, the public will pay to ensure long-term access to water of the quality and quantity that they desire. 

Figure 1: These are the key drivers in anticipating future water/sewer rates. Their relative influence varies by location. Courtesy: Affiliated Engineers Inc.While this may be true, it should not be confused with an unwillingness to conserve water use. The significant distinction is which water uses we are willing to conserve. It appears that there is no strong inclination to conserve water for uses considered essential to health. Thus, at the household level, the most likely accommodation to a call for conservation is in restricted water use for landscape or optional cleaning, such as car washing. A secondary interest would show itself as willingness to participate in subsidy programs for showerhead water restrictions or more efficient toilets—activities that still allow for the basic water-using activity of a household, but with more efficient resource use.  

Meanwhile, studies establish that commercial /industrial/institutional entities do respond to increases in the price of water through reduced use of water supporting non-health-essential functions. This conservation response occurs across the spectrum of utility price points, not just in locations where the cost of water is most expensive; it is a reaction to change in price more than to absolute price. These modified processes and practices differ from those of the residential sphere, which tend to respond episodically to drought conditions rather than by instituting fundamental ways of reducing water use. In the commercial/industrial/institutional setting it is possible to more than offset cost increases with conservation. 

Water use efficiency in code, building rating systems

Figure 2: While project water/sewer costs remain smaller than energy costs, the diverging cost of water rates has elevated its importance in the design process. Courtesy: Affiliated Engineers Inc., based on Consumer Price Index dataIn the past 20 years, water efficiency has been a less urgent cost issue, and thus codes and building rating systems have focused on enabling greater energy efficiency. Consequently, there has been measured and slow research to examine  the real or perceived health risks associated with water reuse as part of creating a path for safe water reuse. The International Association of Plumbing and Mechanical Officials (IAPMO) has made significant updates to the uniform plumbing codes (UPC), including issuing the first Green Plumbing and Mechanical Code Supplement in 2012. However, the UPC covers only a fraction of the water usage in buildings, and many states and local governments have yet to adopt the new code. Water use related to nonhuman consumption is only beginning to be addressed in the codes. 

ASHRAE 191P: Standard for the Efficient Use of Water in Building, Site, and Mechanical Systems is a proposed standard that works to address water usage in buildings holistically. ASHRAE 191P is meant to be a minimum standard with high-performance water usage governed by ASHRAE 189.1: Standard for the Design of High Performance, Green Buildings. ASHRAE 191P governs:

  • Site water usage
  • Greywater
  • Plumbing systems
  • HVAC systems
  • Appliances
  • Process equipment

The standard is being developed in cooperation with the American Society of Plumbing Engineers (ASPE) and the U.S. Green Building Council. A first draft of the proposed standard was issued for public review in October 2012, and review comments are currently being incorporated into a second iteration. 

Figure 3: A 2003 analysis of California commercial sector water use documents the levels of cost-effective water use reduction in key standard industry codes. Courtesy: Affiliated Engineers Inc., based on Pacific Institute dataLEED 2009 for Healthcare introduced prerequisites and credits for process loads, food service equipment, and cooling towers, as well as submetering water usage. This approach has been expanded in LEED v4 (November 2013 release). However, even with a gaining presence in the marketplace, it is estimated that approximately one-third of new commercial construction is designed to LEED standards.

The Living Building Challenge, a nascent program with three buildings that have achieved “living” status, works to press and inspire the design community to move beyond LEED. Comprehensive in its reach of issues, it calls for net-zero water buildings. Here, participating building owners work to use only water that can be captured on-site and to safely process and retain all of it on-site once that water is used. Stormwater also must be managed naturally and within the project site. 

Regardless of efforts to advance regulation to allow for water reuse and recycling and of the progress of building rating systems to guide a more aggressive path, some contrary legislative anachronisms exist. Fifteen western states’ constitutions, statutes, and case law are tied to the prior appropriation doctrine, a mid-19th-century concept that does not recognize water rights as connected to land ownership, but to use (and prior use). Those who argue that these laws do not benefit contemporary needs reference recent case law that promises movement toward enhanced ability to manage water to better serve the region’s population and environmental protection needs. 

Water use efficiency in new construction

The first priority in designing for water-efficient buildings is to do what is easiest and most cost-effective. Regardless of building type or geography, this priority is addressed through avoiding water use. Five universally cost-effective examples are:

  1. Reduce lawn size and select plants appropriate to their settings. This can be accomplished without sacrifice to the aesthetic or monetary value of the site. 
  2. Attend to the fundamentals of building orientation and massing to reduce building energy demand. In so doing, these steps work to reduce the size and water use associated with building mechanical systems. 
  3. Engineer building systems for energy efficiency; this will also reduce water use.
  4. Select the right equipment. Energy- and water-efficient equipment can be identified through a combination of relying on the U.S. EPA WaterSense and Energy start programs and through the design team’s own research. In this setting, equipment refers to water fixtures, landscape equipment, kitchen equipment, and scientific and medical equipment. 
  5. Procure the right amount of equipment. Some building use lends itself well to shared locations for some equipment with the consequence being reduced water and energy use (and capital investment). Meter and automate water use on the desired schedule and as programmed to meet specific circumstances.

Figure 4: Avoided water (though conservation) and water reuse working together can substantially reduce potable water consumption. Courtesy: Affiliated Engineers Inc.The second priority is to use second generation and inferior (nonpotable) quality water. Strategies include:

  • Access the availability and cost of reuse water sources, looking for reduced cost combined with appropriate quality and quantity to support project reuse opportunities. Alternative water sources can be found both in and outside of the building. These include cooling coil condensate waste water, desalinated water, equipment/system wastewater, fire pump testing water, foundation drain water, groundwater, municipal treatment wastewater, roof water, surface water, and stormwater. 
  • Reuse water within the building project. This dictates water quality and quantity (including schedule of quantity over a year) that matches between donor water and use that can employ this water. Building water-consuming uses that can easily reuse water range from the kitchen and laundry room to the mechanical systems and central plant. By way of strategy, the best success comes with working to first match large sources and large water-consuming activity. 
  • Identify reuse water opportunities outside of the building project that can consume the building project’s wastewater. Secure those opportunities rather than releasing good quality water to the municipal sewer system. 

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