Earning LEED 2009 Water Efficiency credits

Meeting LEED's Water Efficiency Credit 3-Water Use Reduction is no longer a sure thing, even for commercial office buildings.

By Ben Biada, PE, LEED AP, Advanced Engineering Consultants, Columbus, Ohio March 17, 2010


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In today’s construction industry, it seems that just about every project is attempting to achieve U.S. Green Building Council (USGB) LEED certification. Now that LEED v3 (2009) has been released, the bar has been raised on what the USGBC considers an environmentally friendly building, especially when it comes to Water Efficiency (WE) Credit 3—Water Use Reduction. (For the purposes of this article, the discussion will focus on typical office buildings, as attempting to discuss too many building types would lead to a rather lengthy discussion.)

Previously, under LEED v2.2 NC , it was very easy to obtain the maximum amount of LEED points for WE Credit 3 by simply installing low-flow lavatory faucets, low-flow urinals, and dual-flush toilets. In fact, this credit was so easily obtained that, by simply implementing these measures, the technology would also yield an extra credit for exemplary performance under the Innovative Design portion of LEED.

The best part is that the there was no need for the no-water urinals to which owners and maintenance staff are frequently opposed. Because of the three major changes in LEED v3’s WE category, though, it is much more difficult to reach water use reduction targets that were previously obtained by designing only slightly above the bare minimum.

The prerequisite

The first significant change to LEED v3 is the requirement that all projects must meet WE Prerequisite 1: 20% water use reduction . This prerequisite has been implemented to help design engineers focus on a very important environmental concern, the reduction of potable water usage.

The prerequisite also could make it difficult for projects such as high-rise residential, major renovation, or commercial interiors attempting to achieve LEED certification. If, for example, a major renovation consisted mostly of architectural and HVAC changes, it would not be eligible for LEED certification.

Fixture groups

The next significant change from LEED v2.2 to v3 is the implementation of Fixture Groups. Under version v2.2, a simple question on the WE Credit 3 template asked what percentage of male restrooms had urinals. The purpose of this question was to establish how frequently a male could use a urinal as compared to a water closet. (A water closet would still be used if necessary, if you catch my drift.)

Because urinals use significantly less water than a water closet, all an architect had to do was ensure that at least one urinal was in all the common male restrooms within a building. The LEED v2.2 template would then assume that all males would use a urinal, thus resulting in a significant amount of water savings. This may not necessarily be the case if the amount of urinals in a particular restroom is less than the amount of male users at a certain point in time.

The purpose of the Fixture Groups in v3 is to eliminate the confusion of male restrooms with urinals, restrooms with two different types of fixtures (i.e., no-water urinal versus low-flow toilet), or restrooms with different types of users. Fixture Groups require the plumbing engineer to break down the usage of each fixture into specific categories based on user and fixture type.

In a simple office building with similar plumbing fixtures and occupant usage, I typically split the fixture groups into three simple groups: male, female, and total lavatory usage (see Table 1). More detailed categories could be used if building occupants used only particular restrooms or if the restrooms had different fixture types (in the case of a mixed-use building with a restaurant on the first floor that has low-flow urinals and transient users, offices on the next few floors with no-water urinals and full-time equivalent users, and hotel rooms on top floors withdual-flush water closets).

Flow fixture baseline

The third and most significant change from LEED v2.2 NC to v3 is the decrease of the baseline flow value for manual public lavatory faucets. In v2.2, a value of 2.5 gal/min (gpm) was used as the baseline flow rate for most manual lavatory fixtures. All a plumbing engineer had to do was specify flow fixtures with a rating of 0.5 gpm, and a very large amount of water savings could be realized for the lavatory flow fixtures in a building.

In v3 though, the new baseline for public or common space lavatories has been established at a value of 0.5 gpm for manually operated flow faucets, which is the standard value incorporated into the Uniform Plumbing Code and International Plumbing Code.

When specifying metered flow fixtures in a proposed building, the “metered faucet” value of 0.25 gal/cycle (gpc) should be used in your baseline calculation. The difference in the two is that metered faucets = 0.25 gpc while the manual faucet value = 0.125 gpc. (0.5 gpm x 1min/60 sec x 15 sec/cycle = 0.125 gpc). Thus, you would recognize a slight water savings if you specified metered faucets (typically done in large common restrooms).

It should also be noted that the baseline flow fixture value for private use lavatories is v2.2 gpm, which would apply to construction types such as dormitories, hotels, and hospital patient rooms.

Because the baseline value has been reduced to what a plumbing engineer would typically specify, there is very little chance for water reduction on flow fixtures, leaving the flush fixtures responsible for reducing water consumption.

Meeting the WE 20% prerequisite

So what does it take to meet the new 20% requisite? When specifying plumbing fixtures for a LEED project, a plumbing engineer must, at a minimum, specify low-flow urinals and dual-flush valves on water closets. In a typical office building with normal business hours and an assumed male to female ratio of 1:1, these two measures should yield a water use reduction of about 23%, which would meet the prerequisite (assuming that manual flow fixtures will be specified at 0.5 gpm).

Low-flow urinals operate at 0.5 gal/flush (gpf) as opposed to the baseline value of 1.0 gpf. Dual flush valves (battery or electrically powered) work on the simple principle that a full 1.6-gal flush is not always needed. When just liquids and paper waste need to be flushed, a partial flush of 1.1 gal can be used. The flush valves have a sensor that determines that if a user occupies the water closet for more than 60 sec, a full 1.6 gal flush shall be used; conversely, if the user remains in the sensor’s range for less than 60 sec, the partial 1.1 gal flush is employed.

Scoring points

In order to get into the “scoring range” for WE Credit in v3, potable water usage must be reduced by 30%. To get to this level, the use of no-water urinals must be implemented. Using no-water urinals and dual-flush fixtures should yield a water use reduction of about 33%, which would achieve 2 points under LEED NC 2009 (see Table 2).

In lieu of no-water urinals, gray water or rainwater harvesting also could be implemented. (Gray water is untreated wastewater that has not come into contact with toilet waste). This harvested water would be used to flush urinal and water closets, thus reducing to zero the amount of potable water needed for flush fixtures. This would yield water savings above the 45% water reduction level, qualifying for an Innovative Design credit for exemplary performance. Even with using harvested water to flush fixtures, it may still be a good idea to specify no-water urinals, as it would cut down on the amount of pump energy that a harvested system would consume.

While these systems can have a high initial cost, they strongly increase the potential of achieving other LEED points such as WE 2—Innovative Wastewater Technologies and SS 6.—Stormwater Design—Quantity Control.

While LEED v3 has made it increasingly difficult to obtain WE points, I applaud the efforts of the USGBC as it continually challenges architects and plumbing engineers to develop creative solutions that reduce building potable water consumption. Such efforts cannot only reduce the amount of electrical energy a municipality needs to process and distribute potable water, but it also can help to eliminate water shortages in areas where water is scarce. So next time you are involved in a LEED project, remember that the WE rules have changed, but with little bit of design ingenuity, achieving these points are still possible.

Table 1: Fixture group definitions

Group name Annual days of operation Full-time employees Transients Retail % female % male
The fixture groups are defined as male, female, and total lavatory use.
The annual days of operation is derived from an average of 50 work-weeks of 5 days/week.
Source: Advanced Engineering Consultants
Female 240 85 25 150 50 0
Male 240 85 25 150 0 50
Total lavatory use 240 85 25 150 50 50

Table 2: LEED v3 Water Efficiency points

Percentage reduction Points
Designers can obtain up to 5 points for meeting the U.S. Green Building Council LEED Water Efficiency (WE) Credit 3—Water Use Reduction. Source: U.S. Green Building Council
20% Prerequisite
30% 2
35% 3
40% 4
45% Innovative design — 1
Author Information
Biada is a project manager with Advanced Engineering Consultants. He has four years of experience designing mechanical systems for commercial and institutional facilities.

How low can you really go?

Based on my company’s experience, we’ve learned the following with respect to newer ultra-high-efficiency plumbing fixtures.

Dual-flush fixtures are not meant to be retrofitted onto existing water closets, as these valves are typically designed to be paired with a specific water closet to ensure that bowl design will facilitate proper flushing at the reduced water capacity.

Some urinal valve manufacturers market a 1/8 gal/flush (gpf) fixture, which can yield even more water savings. Water closet manufacturers have developed a 1.28 gal full-flush fixture, while some offer a 1.6/0.8 gpf dual-flush fixture. Before using any of these fixtures, however, perform a thorough analysis of the fixture’s capabilities to ensure that proper flushing will occur.