Page 131 - The Engineering Guide to LEED-New Construction Sustainable Construction for Engineers

LEED W ater Ef ficiency 111

USGBC Rating System WE Credit 1
LEED-NC 2.2 lists the Intent, Requirements, and Potential Technologies and Strategies
for LEED 2.2 WEc1.1 and LEED 2.2 WEc1.2 as follows, with modifications to reflect the
changes in LEED 2009:

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

Requirements
(LEED 2009 Option 1 worth two points) Reduce potable water consumption for irrigation
by 50% from a calculated mid-summer baseline case. Reductions shall be attributed to any
combination of the following items:
• Plant species factor
• Irrigation efficiency
• Use of captured rainwater
• Use of recycled wastewater
• Use of water treated and conveyed by a public agency specifically for nonpotable uses
Per LEED 2009, groundwater seepage that is pumped away from building slabs and
foundations may be used for irrigation needs, but only if it is demonstrated that this does
not affect stormwater management systems.
(LEED 2009 Option 2 worth an additional two points) Achieve the requirements for Option
1 and:
LEED 2009 Path 1; Use only captured rainwater, recycled wastewater, recycled greywater,
or water treated and conveyed by a public agency specifically for nonpotable uses for
irrigation.
OR
LEED 2009 Path 2; Install landscaping that does not require permanent irrigation systems.
Temporary irrigation systems used for plant establishment are allowed only if removed
within one year of installation.
Potential Technologies and Strategies
Perform a soil/climate analysis to determine appropriate plant material and design the
landscape with native or adapted plants to reduce or eliminate irrigation requirements.
Where irrigation is required, use high-efficiency equipment and/or climate-based
controllers.

LEED 2009 Calculations and Considerations (WE Credit)
All four credit points are automatically earned if there is no irrigation on the site.
Otherwise, this credit subcagtegory usually requires a series of calculations. For two
points, the calculations must show that the design water use of potable water is less
than 50 percent of a baseline irrigation case. For four points, in addition to having none
of the irrigation water potable, or coming from natural surface or groundwater sources
near the site, the calculations must also show that the design water use of any water for
irrigation is less than 50 percent of a baseline irrigation case.
The calculations are done in two main steps. First a calculation for a baseline (typical)
landscape scenario is performed and then calculations for the design case are performed.