The Water Efficiency (WE) section addresses water holistically, looking at indoor use, outdoor use, specialized uses, and metering. The section is based on an “efficiency first” approach to water conservation. As a result, each prerequisite looks at water efficiency and reductions in potable water use alone. Then, the WE credits additionally recognize the use of nonpotable and alternative sources of water.
The conservation and creative reuse of water are important because only 3% of Earth’s water is fresh water, and of that, slightly over two-thirds is trapped in glaciers. Typically, most of a building’s water cycles through the building and then flows off-site as wastewater. In developed nations, potable water often comes from a public water supply system far from the building site, and wastewater leaving the site must be piped to a processing plant, after which it is discharged into a distant water body. This pass-through system reduces streamflow in rivers and depletes freshwater aquifers, causing water tables to drop and wells to go dry. In 60% of European cities with more than 100,000 people, groundwater is being used faster than it can be replenished.
In addition, the energy required to treat water for drinking, transport it to and from a building, and treat it for disposal represents a significant amount of energy use not captured by a building’s utility meter. Research in California shows that roughly 19% of all energy used in this U.S. state is consumed by water treatment and pumping.
In the U.S., buildings account for 13.6% of potable water use, the third-largest category, behind thermoelectric power and irrigation. Designers and builders can construct green buildings that use significantly less water than conventional construction by incorporating native landscapes that eliminate the need for irrigation, installing water-efficient fixtures, and reusing wastewater for nonpotable water needs. The Green Building Market Impact Report 2009 found that LEED projects were responsible for saving an aggregate 1.2 trillion gallons (4.54 trillion liters) of water. LEED’s WE credits encourage project teams to take advantage of every opportunity to significantly reduce total water use.
The WE category comprises three major components: indoor water (used by fixtures, appliances, and processes, such as cooling), irrigation water, and water metering. Several kinds of documentation span these components, depending on the project’s specific water-saving strategies.
Site plans. Plans are used to document the location and size of vegetated areas and the locations of meters and submeters. Within the building, floorplans show the location of fixtures, appliances, and process water equipment (e.g., cooling towers, evaporative condensers), as well as indoor submeters. The same documentation can be used in credits in the Sustainable Sites category.
Fixture cutsheets. Projects must document their fixtures (and appliances as applicable) using fixture cutsheets or manufacturers’ literature. This documentation is used in the Indoor Water Use Reduction prerequisite and credit.
Alternative water sources. A project that includes graywater reuse, rainwater harvesting, municipally supplied wastewater (purple pipe water), or other reused sources is eligible to earn credit in WE Credit Outdoor Water Use Reduction, WE Credit Indoor Water Use Reduction, WE Credit Cooling Tower Water Use, and WE Credit Water Metering. But the team cannot apply the same water to multiple credits unless the water source has sufficient volume to cover the demand of all the uses (e.g., irrigation plus toilet-flushing demand).
Occupancy calculations. The Indoor Water Use Reduction prerequisite and credit require projections based on occupants’ usage. The Location and Transportation and Sustainable Sites categories also use project occupancy calculations. Review the occupancy section in Getting Started to understand how occupants are classified and counted. Also see WE Prerequisite Indoor Water Use Reduction for additional guidance specific to the WE section.