Understanding LEED® Certification: Part II

Existing Buildings: Operations & Maintenance, Water Efficiency

By Jennifer Easton

April 14, 2011

In the LEED for Existing Buildings: Operations & Maintenance rating system, the Water Efficiency credits can be earned by reducing potable water consumption. Strategies include Water closets, urinals, showerheads, faucets, faucet replacement, aerators, and metering faucets. Energy efficiencies can be gained as well.

This country's public water supply is in high demand. The U.S. Geological Survey estimates that Americans' consumption of public water spiked to over 43 billion gallons per day by 2000. While the Clean Water Act helped the U.S. make major strides in reducing both water consumption and contamination, we are still far from using water sustainably. Applying water-efficient techniques and strategies in our buildings can help us reduce water consumption and avoid depleting this key resource.

The Water Efficiency prerequisites and credits in the LEED for Existing Buildings: Operations & Maintenance rating system are geared toward reducing potable water consumption. Results from this credit category are tangible. Efficiency measures such as low-flow plumbing fixtures, sensors, and automatic controls can reduce water use in average commercial buildings by 30 percent or more. In a typical 100,000-square-foot office building, that adds up to a savings of 1 million gallons per year.

Water efficiency not only helps conserve the earth's precious water resources, but also reduces energy use significantly. When less water is consumed, less water has to be heated, cooled, and distributed. Because water heating in commercial buildings accounts for nearly 15 percent of total building energy use, there is incredible potential to reduce energy consumption along with water.

Furthermore, those savings in resources can translate to cost savings. With water efficiency measures in place, utility savings can represent tens of thousands of dollars per year, depending on local water costs. At that level of savings, many of the technologies behind them have a rapid payback.

Water Efficiency Prerequisite 1:
Minimum Indoor Plumbing Fixture and Fitting Efficiency (Required)

Intent: To reduce indoor fixtures and fittings water use within buildings to reduce the burden on potable water supply and wastewater systems.

Requirements: Potable water use through indoor plumbing fixtures and fittings must be reduced to a level equal to or below the LEED for Existing Buildings: Operations & Maintenance baseline. This baseline depends on the year of completion of the building's indoor plumbing system. Water closets, urinals, showerheads, faucets, faucet replacement aerators, and metering faucets all qualify as fixtures and fittings included in the calculations for this credit.

Potential Strategies: With proper analysis and measurement, you can incorporate high-efficiency plumbing fixtures or fittings into most existing buildings. As a starting point, take into account existing infrastructure, equipment, and overall building function. Measure water use to identify inefficiencies and areas for upgrades. This background research will help determine whether existing plumbing fixtures can be retrofitted with high-efficiency valves and aerators, or whether the fixtures need to be replaced completely. Technologies to reduce potable water use include:

• Automatic fixture sensors or metering controls.
• Flow restrictors or reduced-flow aerators on lavatory, sink, and shower fixtures.
• Low-consumption flush fixtures, such as dual-flush water closets and high-efficiency urinals.
• Dry fixtures, such as nonwater urinals and toilet systems.
• Rainwater or graywater use for nonpotable applications.

Maximize the benefits of water-efficient upgrades by communicating proper usage to building occupants. After all, the fixtures must be used correctly to realize their water-saving potential.

Water Efficiency Credit 1:
Water Performance Measurement (1 to 2 points)

Intent: To measure building and subsystem water performance over time to understand consumption patterns and identify opportunities for additional water savings.

Requirements: Fulfill WE Credit 1 by installing a permanent water meter that measures total potable building water use for the entire building and associated grounds (1 point). Employ submetering for one or more water subsystems to earn an additional point (1 point).

Potential Strategies: The permanent, building-level water meter must measure water consumption from manufacturing processes, cooling towers, occupant-related plumbing fixtures, laundering, dishwashing, indoor and outdoor water features, irrigation, and exterior cleaning.

To earn the second point, in addition to the previous tactics, permanently install metering for one or more of the following water subsystems: irrigation, indoor plumbing fixtures and fittings, cooling towers, domestic hot water, or other process water. Consider targeting subsystems for which metering incentives and rebates might exist or where deduct metering will lessen utility costs by avoiding sewage charges.

Water Efficiency Credit 2:
Additional Indoor Plumbing Fixture and Fitting Efficiency (1 to 5 points)

Intent: To maximize indoor plumbing fixture and fitting efficiency within buildings to reduce the use of potable water and consequent burden on municipal water supply and wastewater systems.

Requirements: Have in place systems that produce an overall reduction in indoor potable water use from the calculated baseline in WE Prerequisite 1. The numberof points earned in this credit depends on the percentage reduction in potable water use.

Potential Strategies: Refer to the section on WE Prerequisite 1 for strategies and methods required to obtain this credit.

Water Efficiency Credit 3:
Water-Efficient Landscaping (1 to 5 points)

Intent: To limit or eliminate the use of potable water, or other natural surface or subsurface resources available on or near the project site, for landscape irrigation.

Requirements: Reduce the amount of potable water used in irrigation. For buildings without substantial vegetation on the grounds, points for WE Credit 3 can be earned by reducing the use of potable water for watering any roof, courtyard space, or outdoor planters, provided this accounts for at least 5 percent of the building site area. Projects with less than 5 percent of garden or planter space are ineligible for this credit. The number of points earned for this credit is determined by the percentage reduction in water usage. Project teams must verify the percentage reduction using specific calculations, outlined in the LEED reference guide for Green Buildings Operations & Maintenance.

Potential Strategies: Employ the following methods to fulfill WE Credit 3:

1. Landscaping choices: Use climate-tolerant plants that can survive on natural rainfall. Contour the landscape area so that site vegetation receives additional water from runoff. Conserve water by limiting areas covered in conventional turf, instead applying techniques such as mulching, xeriscaping, and composting.
   
   
2. Irrigation practices: Schedule watering early or late in the day, when evaporation is minimal, to allow more water to soak into the ground and reach the roots of plants. Check ground moisture levels and weather reports to make water-saving adjustments to irrigation practices. Consider using high-efficiency irrigation technology, such as micro or drip irrigation, moisture sensors, clock timers, and weather data-based controllers.
   
   
3. Nonpotable water use: Use a rainwater collection system to reduce or completely eliminate the amount of potable water used for irrigation. Since rainwater with high mineral content or acidity may damage equipment or plants, be sure to install an adequate method of filtration, using soil or mechanical means, before irrigation.

Water Efficiency Credit 4:
Cooling Tower Water Management (1 to 2 points)

Intent: To reduce potable water consumption for cooling tower equipment through effective water management and/or use of nonpotable makeup water.

Requirements: Fulfill WE Credit 4 by applying one of the following three options:

1. Chemical management: Implement a water management plan for the cooling tower that addresses chemical treatment, bleed-off, biological control, and staff training (1 point).
   
   
2. Nonpotable water source use: Use makeup water that consists of at least 50 percent nonpotable water, such as harvested rain- or stormwater, air-conditioner condensate, or swimming pool filter backwash water (1 point).
   
   
3. Achieve both of the above (2 points).

Potential Strategies: Apply the following techniques to achieve WE Credit 4:

1. Chemical management: Recruit water treatment professionals to administer a program that controls corrosion, scaling, sediment, and biological growth. Effective treatment reduces the need for bleed-off, thus conserving water. When possible, use environmentally friendly treatment chemicals and control devices, such as pulsed power.
   
   
2. Nonpotable water source use: Lessen demand on potable water supplies by using makeup water from nonpotable sources. Ensure that nonpotable sources do not introduce biological contamination or food sources for bacteria into the cooling towers. As it is generally cleaner and colder than other potential sources, condensation from air conditioners is an excellent and efficient alternative to potable water.