The baseline calculations offered in this example show the architect an easy way to accomplish the LEED-NC objective of preparing a baseline, and ultimately, the objectives of the LEED-NC credit for Water Use Reduction. For example, LEED-NC v2.1, which is the basis of this approach, requires submittal of the LEED letter templates, which calculate, based on the occupancy of males, females and fixture type, the TOTAL ANNUAL POTABLE WATER VOLUME for the building. In this calculation, the baseline yields a total usage of 157,950 gallons (Chart 2).

Note that we have estimated the daily use and duration of use for each fixture in this building. LEED-NC specifically states that these criteria are not set; therefore, the architect is required to set them, and usage patterns can be determined in many ways (e.g., working with the owner, talking with occupants, etc.).

Calculating the Design Case

In calculating the Design Case (the specific changes being proposed to this building from a water conservation point of view), we must not change the number of building occupants, the number of work days, or the frequency data.

For our Design Case, let's assume the following:

1. Waterfree urinals will be used.
2. 0.8 gpf pressure-assist water closets will be used.
3. Electronic faucets with low-flow aerators (0.5 gpm) will be used. Plus, the electronics have been factored as reducing sink duration by 20% (to 12 seconds). However, electronic controls on water closets do not receive a reduction in duration, as they are fixed-volume devices (e.g., 0.8 gpf). NOTE: The 20% reduction can be found on page 105 of Reference Guide LEED-NC v2.1. Furthermore, university studies have been conducted into water savings of electronic versus manual faucets.

The calculations shown in Chart 3 use the above fixture types. You can see that a 69% reduction in annual water use for the building is achieved-far greater than the 30% reduction required for this LEED-NC credit. In fact, Water Efficiency Credits 3.1 and 3.2 are cumulatively achieved.