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System Impacts

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A sustainable water system reduces not only overall water consumption but also the associated energy demand. Take steps to optimize the system’s efficiency, implement water conservation measures, and integrate water reuse/recycling strategies.

Conservation Measures

Commercial buildings have significant opportunities to conserve the quantity of water needed for daily operations through thoughtful design of the building plumbing fixtures, landscape, boiler and cooling tower systems, and single-pass cooling equipment.

The Department of Energy Federal Energy Management Program (FEMP) has developed a list of Water Efficiency Best Management Practices, also called "BMPs". These BMPs provide information on key water consuming equipment found in the Federal sector and give strategies to increase operational efficiency and reduce water consumption. The BMPs are a great starting place to learn the options available for water efficiency improvements.

  • BMP #1 - Water Management Planning
  • BMP #2 - Information and Education Programs
  • BMP # 3 - Distribution System Audits, Leak Detection, and Repair
  • BMP # 4 - Water-Efficient Landscaping
  • BMP # 5 - Water-Efficient Irrigation
  • BMP # 6 - Toilets and Urinals
  • BMP # 7 - Faucets and Showerheads
  • BMP # 8 - Boiler/Steam Systems
  • BMP # 9 - Single-Pass Cooling Equipment
  • BMP #10 - Cooling Tower Management
  • BMP #11 - Commercial Kitchen Equipment
  • BMP #12 - Laboratory/Medical Equipment
  • BMP #13 - Other Water Intensive Processes
  • BMP #14 - Alternate Water Sources 

This tool focuses on water applications in office buildings. The related FEMP BMPs are BMP #4, 5, 6, 7, 8, 9, 10, 11 and 14, which are featured in the sections below.

Water used for landscaping and irrigation purposes accounts for close to 20% of a facility’s overall consumption and should be limited as much as possible through xeriscaping, water-efficient systems and schedule optimization. See FEMP BMP #4 and BMP #5.

  1. Reduce the amount of irrigated areas and replace water-intensive plants with native or climate appropriate landscape materials to decrease or completely offset both water consumption and maintenance costs (i.e. fertilizer, pruning, mowing, and landscaping labor).
  2. For landscape areas needing irrigation, incorporate water-efficient systems such as efficient irrigation nozzles or drip irrigation systems that evenly distribute water and minimize losses.
  3. Optimize irrigation schedules and controls to deliver water to the landscape only as needed based on weather conditions.


High efficiency plumbing fixtures (toilets, urinals, faucets, and showers) can lead to significant water savings. FEMP BMP #6 gives some guidance on toilets, and BMP #7 deals with faucets and showerheads.    The following table provides a comparison of standard fixtures versus high efficiency counterparts.

Plumbing Fixture Type

Standard Rating

High Efficiency Rating



1.6 gpf

1.28 – 0.8 gpf

tank, pressure assisted, flush valve, dual flush


1.0 gpf

0.5 – 0 gpf

flush valve, non-water

Private faucets

2.2 gpm

1.5 – 0.5 gpm

manual, sensored, metered

Public faucets

0.5 gpm

0.5 gpm

current plumbing code requires 0.5 gpm flow rate for public restrooms


2.5 gpm

2.0 – 1.5 gpm



Utilizing non-potable water sources, such as grey water, for flushing toilets and urinals further reduces overall potable water consumption. Maintenance of flush valves is imperative, as a constantly running toilet can waste over 200 gallons of water each day.1

Flush valve toilets are typically fitted with diaphragm-style valves.  Piston valves are an alternative to diaphragm valves and have distinct advantages including:

  • Longer life and lower operations and maintenance costs because piston valves contain a screen that prevents debris from entering the inner portion of the valve and are made of more resilient, longer lasting material.
  • Less valve corrosion that results in consistent flush rate over the life of the valve; whereas diaphragm valves tend to degrade more quickly that can cause the flush rate to increase over time.
  • Piston valve retrofit kits are not interchangeable between different flush ratings; whereas diaphragm retrofit kits are universal, meaning a 1.28 gpf valve can be replaced with a 3.5 gpf valve, turning a high efficiency toilet into a high water consuming fixture.
  • Tolerant of low pressure, rated at a minimum pressure of 15 pounds per square inch (psi); diaphragm valves require at least 35 psi to operate.
  • Default in the closed position when the valve breaks; whereas diaphragm valves remain open at failure, leaking water continually until repaired.

Keep in mind that faucets and showers require energy to heat the water to comfortable levels. As a result, reducing the amount of water needed for showering and washing hands also reduces energy use.

As with all plumbing fixtures, maintenance is important to ensure continued water conservation; a leaky faucet dripping at a rate of one drip per second can waste more than 3,000 gallons of water annually.1

1. EPA WaterSense: The Facts on Leaks

Boiler and steam system equipment consume varying quantities of water within large heating systems depending on the size of the equipment, the amount of steam used, and the corresponding amount of condensate returned. As a result, it is important to properly size boiler and steam units according to the facility’s heat and steam requirements. Reducing these requirements leads to less makeup water needed in the system. Water supply and chemical use can be reduced up to 70% by recycling condensate for reuse within the boiler and steam units.1 Similarly, automatic blow-down systems based on detection of boiler water quality will more efficiently manage the removal of accumulated solids and/or sludge without wasting water. Control scale buildup on heat transfer surfaces by using chemical treatment and catalyst-based scale prevention. Reference FEMP BMP #8 for this and other information about Boilers and Steam Systems.

Single-pass (or once-through) cooling equipment uses water for only one cycle before subsequently discharging it. Examples of this equipment include condensers, air compressors, degreasers, vacuum pumps, ice machines, and air conditioners. In order to maximize water savings, single-pass systems should be eliminated altogether or be replaced or modified to operate on a closed-loop that recirculates water instead of discharging it. If a closed-loop alternative is not feasible, implementing an automatic shut-off valve and reusing the discharged water for non-potable situations are sustainable alternatives. To remove the same heat load, single-pass systems use 40 times more water than a cooling tower operated at five cycles of concentration. To maximize water savings, single-pass cooling equipment should be either modified to recirculate water or, if possible, should be eliminated altogether. FEMP BMP #9 has more suggestions for optimizing use of single-pass cooling equipment.

Water leaves the cooling tower system through evaporation, blow-downdrift, and basin leaks and overflows, and therefore has to be replaced. Since cooling towers by nature dissipate heat from recirculating water through evaporation, reducing the quantity of water lost to evaporation can be achieved through improving the energy efficiency of the systems being cooled. Blow-down, however, should be carefully monitored and controlled with conductivity meters to ensure dissolved solid concentrations are regulated without wasting water. Implementing baffles and drift eliminators limit the water losses attributed to mist being carried from the system, while checking float control equipment and valves ensures basin leaks or overflows are properly avoided. Chemical treatment and alternative water treatment (AWT) technologies control scale buildup and increase cycles of concentration. Cooling tower management is covered by FEMP BMP #10.

Alternate Water Sources

Alternate water sources are not from freshwater such as surface or groundwater. Alternate water is typically collected and stored on-site and then reused in non-potable applications.

Examples of on-site sources of alternative water include:

  • Rainwater
  • Stormwater
  • Greywater
  • Air-conditioning condensate
  • Fountain discharge
  • On-site reclaimed wastewater
  • Process equipment discharge
  • Cooling tower blow-down

Examples of alternate water applications include:

  • Cooling tower makeup
  • Landscape irrigation
  • Pollution control
  • Toilet and urinal flushing
  • Fountain/pond makeup

Applications depend on the level of contaminates present and on State and local legislation. Check with local jurisdictions for any regulations or incentive programs that should guide water system projects.

Harvesting systems capture alternate water sources, provide adequate treatment typically for non-potable applications to offset the consumption of potable water supplied to the building. Rainwater harvesting typically involves collection from the roof of the building. Coupled with a green roof, additional treatments to rainwater might not be necessary before reuse. Stormwater harvesting involves collection of water accumulated from access rain on surface ponds or basins and requires additional treatment. While this source is not safe for drinking in the office environment, popular end uses include landscape irrigation, cooling tower makeup, and toilet flushing to offset potable water consumption and wastewater discharge.

Greywater is the water stemming from processes such as showers, hand basins, or kitchen sinks but does not contain any human waste. Reusing greywater typically involves some form of basic solid filtration and microbial digestion treatments which permit the resource to be utilized in landscape irrigation and toilet flushing applications, thus reducing total potable water consumption. Greywater harvesting systems should comply with local health codes and ordinances.

Energy Use

Water efficiency measures do more than conserve water; they conserve a significant amount of energy as well. Federal facilities use sixty billion Btu of energy annually to process, heat, and distribute water throughout buildings. Of that, over 98 percent of that energy is used for heating water.1 Similarly on a national scale, eight percent of U.S. energy demand goes to treating, heating, and pumping water – equivalent to powering five million homes for an entire year.2 Conversely, it takes 3,000 to 6,000 gallons of water annually to power just one 60-watt incandescent bulb for 12 hours per day.3 Implementing a sustainable water system that leads to measurable water conservation, as a result, further benefits the facility’s overall energy management plan and reduces associated costs. Water conservation also means that less need be treated in the first place, reducing the embodied energy associated with purification and distribution across our water infrastructure.

Consider whether solar hot water heating is appropriate. The Energy Independence and Security Act of 2007 requires that no less than 30 percent of the hot water demand for each new Federal building or major renovation must be met through solar hot water, if lifecycle cost-effective.

1. Whole Building Design Guide (WBDG): Water Conservation2. EPA Buildings and their Impact on the Environment: A Statistical Summary3. EPA: Water Resources

Best Practices and Strategies

Replace standard plumbing fixtures with high efficiency fixtures. Specify WaterSense labeled products for equipment replacements. Limit the need for landscape irrigation by xeriscaping.
Implement water efficient irrigation equipment such as drip or micro irrigation and   advanced weather based controls for landscaping that needs supplemental water. Use alternate non-potable water sources such as gray water, rainwater, air handling unit condensate, cooling tower blow-down or discharge from other processes for landscape irrigation and toilet flushing. Sub-meter and monitor water use to detect and fix leaks in the system.
Use biological waste treatment systems to treat waste on site. Commission water and sewer systems as part of the project quality assurance process. Apply the FEMP Water Efficiency Best Management Practices.