Page 144 - The Engineering Guide to LEED-New Construction Sustainable Construction for Engineers

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(WEp1) for the 20 percent reduction, and then the WE credit 3 (WEc3) for two, three,
and four points for 30, 35, and 40 percent reductions, respectively.
WE Credit 3: Water Use Reduction

USGBC Rating System WE Credit 3
LEED-NC 2.2 lists the Intent, Requirements, and Potential Technologies and Strategies
for WEc3 as follows, and as modified to be applicable to LEED 2009.

Intent
Maximize water efficiency within buildings to reduce the burden on municipal water
supply and wastewater systems.
Requirements
Employ strategies that in aggregate use less water than the water use baseline calculated for
the building (not including irrigation) after meeting the Energy Policy Act of 1992 fixture
performance requirements (or as modified to the 2006 UPC and IPC in LEED 2009).
Calculations are based on estimated occupant usage and shall include only the following
fixtures (as applicable to the building): water closets, urinals, lavatory faucets, showers and
kitchen sinks (with prerinse spray valves also included in LEED 2009).
Potential Technologies and Strategies
Use high-efficiency fixtures, dry fixtures such as composting toilet systems and non-water
using urinals, and occupant sensors to reduce the potable water demand. Consider reuse of
stormwater and greywater for non-potable applications such as toilet and urinal flushing
and custodial uses.

Calculations and Considerations (WE Prerequisite 1 and WE Credit 3) LEED 2009
The calculations for WE prerequisite 1 and WE credit 3 are very similar to the calculations
for Option 1 of WE credit 2, with four additional types of fixtures added: lavatory
faucets, showers, prerinse spray valves, and kitchen sinks. Bathtubs are not addressed,
but the author assumes that all residential facilities that have bathtubs are modeled as
if they have a shower head, and the calculations are based on the shower head flow. The
intention of the credit is not to reduce the volume of water as needed for proper bathing
or food preparation and cleanup, but to limit the wasted water from unused faucet
flow. Also, not addressed in these credits are dishwashers and clothes washers.
Many water usage calculations for other purposes are based on the number of fixtures
in a building. The calculations for WE prerequisite 1 and WE credit 3 are not based on the
number of fixtures, but rather on the number of users, as was done in the WE credit 2
calculations and will also differentiate between the number of male and female users in
case they are not equal. However, in most cases, the default assumption is that the facility
is gender-neutral, with one-half of the users male and the one-half female.
Commercial and Institutional Uses The total annual water closet and urinal usage rates
(in number of times used per year) are again estimated using the FTE estimates as
developed in SSc4.2, defining the following:

FTE Full-time equivalent building occupant during shift j.
j
FTE Full-time equivalent building occupancy of employee i during shift j. This is
j,i
equal to 1 for a full-time employee and is equal to the normal hours worked
(less than 8) divided by 8 for a part-time employee. Obviously, this will need
to be modified if shifts are different from the standard 8 h.