Page 143 - The Engineering Guide to LEED-New Construction Sustainable Construction for Engineers

LEED W ater Ef ficiency 123

and substituting DO for FTE, Eq. (3.2.2) simplifies to Eq. (3.2.7) such that the estimated
total annual number of water closet usages is
TWCU = 365 × 5 × DO For residential uses (3.2.7)

Equations (3.2.4) through (3.2.6) can again be used for the Option 1 calculations relating
to these residential uses. In cases where there will be no alternative nonpotable water
used for the water closets, the calculations can be further reduced to the following
simple equation for obtaining Option 1 WE credit 2:

WCR for WCR in gallons per fl ush, for typical mixed-gender
i ≤ 050 i
.
16 residences with only potable water to water closets (3.2.8)
.
Option 2 Option 2 of WE credit 2 is for providing on-site wastewater treatment that is
treated to tertiary standards and infiltrated and/or reused on-site. The calculations use
the design wastewater generation rate (BWD) as calculated in Eq. (3.2.5) (or as applicable
for residential facilities). Let TBW be the annual volume of blackwater treated and
infiltrated and/or reused on-site. Option 2 of WE credit 2 may then be obtained if the
following is true:

TBW ≥ . 050 (3.2.9)
BWD
The calculations for Option 2 do not include nonpotable waters used for flushing toilets
in the numerator unless these nonpotable waters are part of the treated and reused
blackwater generated (i.e., part of the TBW). In addition to the calculations, the
submittals must include a narrative and additional information on how, and how much
of, the blackwaters are treated, infiltrated, and/or reused on-site.

Special Circumstances and Exemplary Performance (WE Credit 3)
As mentioned previously, if the local jurisdiction defines blackwater to include other
wastewaters, then the volumes of these wastewaters generated should be included in the
total baseline and design blackwater generation rates (BWB and BWD) for both options.
This should be appropriately noted in the submittals. If there are special circumstances
for this credit, a narrative must be submitted describing these circumstances.
There is an EP point available for this credit for each option based on the following
criteria:
• Option 1: There is no potable water used for sewage conveyance (BWD = GW).
• Option 2: 100 percent of these wastewaters are treated to tertiary standards and
infiltrated or reused on-site (TBW = BWD).

3.3 WE Credit Subcategory 3: Water Use Reduction
The intention of this credit subcategory is to reduce the use of potable water for indoor
use. In LEED 2.2, WEc3.1 is worth one point for a 20 percent reduction and WEc3.2 is
one point in addition to the point for WEc3.1 for a 30 percent reduction. In LEED 2009,
overall building water use reduction is addressed under the required WE prerequisite 1