LEED Water Efficiency
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
- 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 "pee's 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:
61% water use reduction
- WEc1.1 Water Efficient Landscaping Reduce by 50%
This credit is directed towards selecting a site that can easily accommodate LEED parameters. Remember the agencies involved with each of the parameters. The following 6 types of sites are NOT to be developed:
- Prime Agricultural Farmland - this only means that the USDA has to deem it a prime farmland; just because the previous developer had cows and grew corn on the property does not deem it prime farmland.
- Within 100 feet of a wetland as decided by 40 CFR (Code of Federal Regulations)
- Within 50 feet of a body of water
- Habitat of an endangered species; this includes plants and animals alike!
- Below 5 feet above the one hundred year flood plain. Read this carefully. Imagine the one hundred year flood plain. Now go up five feet. You can't be developing on a site lower than this. Also this flood plain is determined by FEMA - important to know.
- Public Parklands, unless replacing with an equal or larger piece of parkland elsewhere
Applicable standards or agencies: USDA, CFR, FEMA
- WEc1.2 Water Efficient Landscaping No Potable Water Use or No Irrigation
This credit is directed towards selecting a site that can easily accommodate LEED parameters. Remember the agencies involved with each of the parameters. The following 6 types of sites are NOT to be developed:
- Prime Agricultural Farmland - this only means that the USDA has to deem it a prime farmland; just because the previous developer had cows and grew corn on the property does not deem it prime farmland.
- Within 100 feet of a wetland as decided by 40 CFR (Code of Federal Regulations)
- Within 50 feet of a body of water
- Habitat of an endangered species; this includes plants and animals alike!
- Below 5 feet above the one hundred year flood plain. Read this carefully. Imagine the one hundred year flood plain. Now go up five feet. You can't be developing on a site lower than this. Also this flood plain is determined by FEMA - important to know.
- Public Parklands, unless replacing with an equal or larger piece of parkland elsewhere
Applicable standards or agencies: USDA, CFR, FEMA
- WEc2 Innovative Wastewater Technologies
This credit is directed towards selecting a site that can easily accommodate LEED parameters. Remember the agencies involved with each of the parameters. The following 6 types of sites are NOT to be developed:
- Prime Agricultural Farmland - this only means that the USDA has to deem it a prime farmland; just because the previous developer had cows and grew corn on the property does not deem it prime farmland.
- Within 100 feet of a wetland as decided by 40 CFR (Code of Federal Regulations)
- Within 50 feet of a body of water
- Habitat of an endangered species; this includes plants and animals alike!
- Below 5 feet above the one hundred year flood plain. Read this carefully. Imagine the one hundred year flood plain. Now go up five feet. You can't be developing on a site lower than this. Also this flood plain is determined by FEMA - important to know.
- Public Parklands, unless replacing with an equal or larger piece of parkland elsewhere
Applicable standards or agencies: USDA, CFR, FEMA
- WEc3.1 Water Use Reduction Reduce by 30%
This credit is directed towards selecting a site that can easily accommodate LEED parameters. Remember the agencies involved with each of the parameters. The following 6 types of sites are NOT to be developed:
- Prime Agricultural Farmland - this only means that the USDA has to deem it a prime farmland; just because the previous developer had cows and grew corn on the property does not deem it prime farmland.
- Within 100 feet of a wetland as decided by 40 CFR (Code of Federal Regulations)
- Within 50 feet of a body of water
- Habitat of an endangered species; this includes plants and animals alike!
- Below 5 feet above the one hundred year flood plain. Read this carefully. Imagine the one hundred year flood plain. Now go up five feet. You can't be developing on a site lower than this. Also this flood plain is determined by FEMA - important to know.
- Public Parklands, unless replacing with an equal or larger piece of parkland elsewhere
Applicable standards or agencies: USDA, CFR, FEMA
- WEc3.2 Water Use Reduction Reduce by 35%
This credit is directed towards selecting a site that can easily accommodate LEED parameters. Remember the agencies involved with each of the parameters. The following 6 types of sites are NOT to be developed:
- Prime Agricultural Farmland - this only means that the USDA has to deem it a prime farmland; just because the previous developer had cows and grew corn on the property does not deem it prime farmland.
- Within 100 feet of a wetland as decided by 40 CFR (Code of Federal Regulations)
- Within 50 feet of a body of water
- Habitat of an endangered species; this includes plants and animals alike!
- Below 5 feet above the one hundred year flood plain. Read this carefully. Imagine the one hundred year flood plain. Now go up five feet. You can't be developing on a site lower than this. Also this flood plain is determined by FEMA - important to know.
- Public Parklands, unless replacing with an equal or larger piece of parkland elsewhere
Applicable standards or agencies: USDA, CFR, FEMA
- WEc3.3 Water Use Reduction Reduce by 40%
This credit is directed towards selecting a site that can easily accommodate LEED parameters. Remember the agencies involved with each of the parameters. The following 6 types of sites are NOT to be developed:
- Prime Agricultural Farmland - this only means that the USDA has to deem it a prime farmland; just because the previous developer had cows and grew corn on the property does not deem it prime farmland.
- Within 100 feet of a wetland as decided by 40 CFR (Code of Federal Regulations)
- Within 50 feet of a body of water
- Habitat of an endangered species; this includes plants and animals alike!
- Below 5 feet above the one hundred year flood plain. Read this carefully. Imagine the one hundred year flood plain. Now go up five feet. You can't be developing on a site lower than this. Also this flood plain is determined by FEMA - important to know.
- Public Parklands, unless replacing with an equal or larger piece of parkland elsewhere
Applicable standards or agencies: USDA, CFR, FEMA