LEED Water Efficiency

Water Drops
Fig 1: Water Drops (Photo: Steve took it)

According to the LEED Reference Manual, a typical 100,000 sf building can save up to 1 million gallons of water in a year if it uses low-flow fixtures, sensors and automatic shutoffs. This sentence alone clearly explains the importance of water efficiency and the demand a building can place on our water resources.

The following breakdown conforms to LEED v3.0. Changes include a new prerequisite that water use be reduced by 20%, and the WEc3 was expanded to 30%, 35% and 40% respectively. Aside from the added prerequisite, the points allotted to Water Efficiency were doubled from 5 to 10 in the new scorecard. Reference the LEED Scorecard for more information on points per each credit and percentage achieved.

Remember to check the USGBC's downloadable forms or the LEED RPC's page? to see which Regional Priority Credits can be counted as added points towards certification in your project's zip code.


Breakdown of Each Credit in Water Efficiency - LEED v3.0

Use the "Show/ Hide" buttons below to help yourself memorize these sections. This is a great tool for double checking your hand-written list of the LEED v 3.0 Scorecard.

  • WEp1 Water Water Use Reduction Reduce by 20%

This credit is directed towards water use reduction of both flush and flow fixtures. This includes reduced flow water closets, low-flow lavs (sinks), electronic faucets, use of air pressure to increase flow.

  • Important to know what information you need to perform a flush usage calculation: flush fixture: daily uses, flowrate, duration (a flush), occupants (assume # men = # women), which will equal water use per that type of flush fixture.
  • Calculating water usage for a flow fixture is slightly different, but just as easy to follow: ''daily uses, flowrate, duration (seconds), auto controls (% savings), number of occupants
  • The LEED AP Exam may ask for a calculation of water use: remember 2 pees and 1 poo per person per day. Men will use urinals 2x and toilets 1x on average, women will use the toilet all 3x's - sounds silly, but people forget. This could be asked as a small calculation on the exam.
  • It's important to understand units: flowrate = gallons per flush for flush fixtures which is typically higher in water closets compared to urinals. For flow fixtures (sinks) flowrate = gallons per second think, all flushes are uniform (for example 1.6 gal per flush), but haven't you noticed the automatic sensors that shut off after you've moved your hands? Or the units that shut off automatically after 10 seconds? This is why it's important to remember the above assumptions when performing any calculations for the exam.
  • These people (occupants) will be washing their hands each time they use the restroom, so you may need to remember this for calculations as well.



Applicable standards or agencies: EPA Act 1992,

This table is a great example of what you should be able to put together in an exam, given the following information: number of occupants (assume # men = # women), fixture types, and flowrates of given fixtures. See below for a completed table of a design case compared to the baseline case:

Table 1: Design Flush Calculations
Fixture Type Daily Uses Flowrate (GPF) Occupants Sewage Generation
Low-Flow Water Closet (Male) 0 1.1 150 0
Low-Flow Water Closet (Female) 3 1.1 150 495
Composting Toilet (Male) 1 0 150 0
Composting Toilet (Female) 0 0 150 0
Waterless Urinal (Male) 2 0 150 0
Waterless Urinal (Female) 0 0 150 0

So this leaves us with 495 gallons used per day in the design case. When comparing to the baseline case, we keep the same uses per day, same # occupants, the same total # annual work days, so really the daily use is the same ratio to the baseline as the annual use. For some reason, the reference book shows an example comparing annual usage, but the ratio should be the same. I choose to stop at the daily use.

Ok, so moving on to the baseline case, we will get a daily rate, and then [1 - (design case) / (baseline case)] = % of water use reduction. See why I choose to stop at daily rate? The multiplication factors just divide out; same ratio.

Table 2: Baseline Flush Calculations
Fixture Type Daily Uses Flowrate (GPF) Occupants Sewage Generation
Water Closet (Male) 1 1.6 150 240
Water Closet (Female) 3 1.6 150 720
Urinal (Male) 2 1.0 150 300
Urinal (Female) 0 1.0 150 0

Here, our daily volume is 1,260 for the baseline case. So, taking the two values calculated, we get the following:

1 - {495\over 1260} =
1 - .39 =
.61 =

61% water use reduction

  • WEc1.1 Water Efficient Landscaping Reduce by 50%

This credit is aimed at reducing the baseline potable water consumption for a site by 50%. There are a few ways this reduction could be achieved:

  1. The type of plant used will have a species factor that helps or hurts the calculation based on the amount of water the plant needs to survive. Hearty plants from desert-lands are suggested.
  2. Irrigation of the site can maximize the water efficiency with less water than a typical project
  3. Rainwater could be stored on site for use in irrigation. This may not work as well in areas that do not get a lot of rain.
  4. Use of recycled wastewater; recycling on the project site can be difficult and costly to incorporate into the design.
  5. Use of treated wastewater conveyed by a public agency; very difficult to achieve, but is feasible in some cases depending on if the city treats the water and makes it readily available.

You should be able to define potable water, which is fancy for water that is good enough to drink. The theory behind this credit is: why use perfectly good drinking water on your plants when they'll thrive just as well with recycled wastewater? Have you ever walked by a landscaped area and seen the small sign that politely tells you not to drink the water from the sprinklers? Now you know why!

Possible Points: 2 Points.
Applicable standards or agencies: USDA, CFR, FEMA

  • WEc1.2 Water Efficient Landscaping No Potable Water Use or No Irrigation

This credit is very straightforward. The proposed landscaping plan must use 100% non-potable water. It's important to remember that you cannot achieve WEc1.2 without first achieving WEc1.1 as these two credits go hand in hand. Here are the requirements for this credit:

  1. Achieve WEc1.1.
  2. Use only captured rainwater, recycled wastewater (think the water from sinks, or condensate from HVAC - smart!), recycled greywater (have you ever driven around campgrounds and seen the greywater signs - that's RV lingo for sewage), or water that's been treated by a public agency for non-potable uses for irrigation.

---OR---

  1. Design a landscaping system that doesn't need permanent sprinkler or irrigation systems. The construction project may decide to install a temporary system to help grow the landscape within the first year of construction (but must be removed after that first year to be eligible for this credit)

Applicable standards or agencies: None
Potential Calculations: There could be a problem on your test asking you about the factors that lead to the irrigation calculation:

  1. Species Factor: ks, this is a variable that depends on what type of plant is being used, and factors in to the amount of required water to sustain the landscape of the project (think cactus vs. a fern for example)
  2. Density Factor: kd, this is the variable that explains how closely the plants are to one another. Planting the groundcover cose together is better for this calculation
  3. Microclimate Factor: kmc, tells about the specific climate of the property. For example, does a nearby building provide shade for most of the day? Are the plants on the roof?
  4. Information will stay the same for Trees, Shrubs, Groundcovers, Mixed, Turfgrass (potential Landscape types): The total site area and microclimate factor.

Terms to Know:

  1. Evapotranspiration Rate: Think about the word here. It looks like a mix of Evaporate and Transpire. ETo is normally calculated in July, the worst case scenario in America. It's important to understand this rate when calibrating the weather in your region.

Possible Points: 4 Points

  • WEc2 Innovative Wastewater Technologies

Think of toilets and urinals when you hear the word "wastewater" because that's all this credit is referencing. A big light should go off in your head with the number 50% attached to it. This credit can be achieved in one of two ways:

  1. Reduce Potable water for sewage by 50%

---OR---

  1. Treat 50% of water on site to tertiary standards

Here are some important facts and terms to know for this credit:

  1. You should consider this credit as a means of calculating the water that leaves the building via flush fixtures: toilets, urinals, composting toilets, etc.
  2. Let's be honest, treating 50% of the water onsite is extremely difficult. Most projects would go for the reduction option.
  3. Flush FIxtures: These are fixtures in the design that flush. Easy.
  4. Flush Average: This one's critical: the flush average is per day for the occupant type, not per the # of fixtures. The full-time equivalent (FTE) is 2 pee's and 1 poo per person, or 3 per person. (see the first pre-req for more information on the subject).
  5. Remember guys stand to pee (hence the urinal calculations) and girls sit to pee. This sounds silly, but it's important to remember for the calculations that are required to achieve this credit. Low-flow urinals aren't enough to increase the wastewater reduction percentage alone. It's usually a good idea to consider low flow urinals and toilets in conjunction for sufficient calculations to achieve this credit.
  6. See the table above for the Pre-req, just consider flush fixtures only.

Possible Points: 2 Points.
Applicable standards or agencies: E'PACT 92 which is a plumbing standard

  • WEc3.1 Water Use Reduction Reduce by 30%

Water Use Reduction is an extension of the Pre-Requisite for this portion of the credits in LEED. In this section, the project must reduce water use by 30% to earn the 2 credits associated with this credit.

See the pre-requisite portion for specific calculations that would be required to prove your project should earn this credit.

Applicable standards or agencies: E'PACT 92, same as the Wastewater Reduction Credit.
Possible Points: 2 Points

  • WEc3.2 Water Use Reduction Reduce by 35%

Water Use Reduction is an extension of the Pre-Requisite for this portion of the credits in LEED. In this section, the project must reduce water use by 35% to earn the 3 points associated with this credit.

See the pre-requisite portion for specific calculations that would be required to prove your project should earn this credit.

Applicable standards or agencies: E'PACT 92, same as the Wastewater Reduction Credit.
Possible Points: 3 Points

  • WEc3.3 Water Use Reduction Reduce by 40%

Water Use Reduction is an extension of the Pre-Requisite for this portion of the credits in LEED. In this section, the project must reduce water use by 40% to earn the 4 points associated with this credit.

See the pre-requisite portion for specific calculations that would be required to prove your project should earn this credit.

Applicable standards or agencies: E'PACT 92, same as the Wastewater Reduction Credit.
Possible Points: 4 Points


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