© 2007 Jonathan Ochshorn.contact | homepage | index of selected writings |
Following is my summary and critique of the "Water Efficiency" section of the LEED 2.2 New Construction Reference Guide, Second Edition, Sept. 2006. My commentary on the Reference Guide can be found in the red boxes below, and within each of the chapters linked immediately above.
Two points are possible, depending upon the degree of compliance: 1 point for achieving a 50% reduction, and 2 points for complete elimination of potable water for landscape irrigation, based on calculation of typical July "baseline" water usage. Calculations include consideration of plant species, efficiency of irrigation, use of harvested rainwater or recycled wastewater, or the use of specially treated public non-potable water. For 2 points, one still must satisfy the criteria of a 50% minimum reduction in water use, as well as using only harvested rainwater (e.g., from roofs), recycled wastewater or graywater, or specially treated public non-potable water. Of course, one can also get the 2 points by using plants that require no irrigation.
It seems strange to award these points in climate regions where no irrigation is necessary. It's also not clear why a 50% reduction of water use is required to achieve the second "bonus" point, when all of the water used could conceivably be harvested from the roof (i.e., have no impact on the use of potable water).
Some suggestions for compliance: use grass ("turf") only "for functional benefit..."; use efficient irrigation systems; avoid any irrigation of plants/turf from November to April and of shrubs from September to June; use native or adapted plants; use metal, clay, or concrete roof materials when harvesting rainwater to avoid contamination of the water.
The benefits of reducing wastewater are twofold: first, potable water used to generate wastewater is reduced; second, less wastewater is discharged into water bodies. There are two ways to satisfy this credit, corresponding to the benefits cited. Either cut potable water use (for sewage conveyance) in half by using water-conserving fixtures or non-potable water; or treat half of the wastewater generated on-site to so-called "tertiary" standards (the highest level of wastewater treatment) and use or discharge this treated water on-site.
Some of the strategies suggested include:
Aquatic systems to treat wastewater using biological organisms (bacteria, plants, fish, etc.);
Composting toilets using no water (treating waste through microbiological means);
Non-water-using urinals using a buoyant liquid above the urine zone to block gas and odor.
One or two points are awarded corresponding to 20% or 30% reduction in potable water use, not counting irrigation. This reduction is measured from the "baseline" condition which is defined per Energy Policy Act of 1992 fixture performance requirements. Only water closets, urinals, lavs, showers, and kitchen sinks need comply. The 1992 standards are as follows:
|water closet||1.6 gallon per flush (gpf)|
|showerhead||2.5 gallon per minute (gpm) at 80 psi|
|metering faucet||0.25 gallons/cycle (manual on/auto off)|
Strategies include high-efficiency fixtures or dry fixtures (see Credit 2), sensors or metering faucets, and reuse of stormwater/graywater.
The idea that profitability is the driving force for implementation of these guidelines is constantly reiterated in the LEED commentary. For example, building owners are warned here that reusing graywater might not be a realistic strategy: "While graywater collection and storage may not be a water reduction method that many owners and designers have the opportunity to include in their projects [presumably because of high cost and/or local code restrictions], high-efficiency plumbing fixtures are."
First posted Nov. 2, 2007; last updated 25 January, 2008 [minor re-formatting]