The intent of this credit is to reduce the amount of potable waterPotable water meets or exceeds EPA's drinking water quality standards and is approved for human consumption by the state or local authorities having jurisdiction; it may be supplied from wells or municipal water systems. used for flush fixtures and to minimize the amount of wastewater conveyed to the municipal system. For credit compliance, you have two options:
Option 1: Reduce the quantity of potable water used for flush fixtures (water closet and urinals only) by 50%. You have two ways to make this reduction:
Option 2: Treat 50% of wastewater onsite to tertiary standards and infiltrate it, or reuse the treated wastewater onsite.
To determine your percentage reduction, compare a baseline case with the design case. Note that the baseline for WEc2 is not the same as the baseline for WEc3: Water Use Reduction. Whereas WEc3 count flow (shower, lavatory and kitchen sink) and flush fixtures (toilets and urinals), WEc2 only counts toilets and urinals.
The calculations for wastewater use are based on the number of full-time equivalentFull-time equivalent (FTE) represents a regular building occupant who spends 40 hours per week in the project building. Part-time or overtime occupants have FTE values based on their hours per week divided by 40. Multiple shifts are included or excluded depending on the intent and requirements of the credit. (FTEFull-time equivalent (FTE) represents a regular building occupant who spends 8 hours a day (40 hours a week) in the project building. Part-time or overtime occupants have FTE values based on their hours per day divided by 8 (or hours per week divided by 40). Transient Occupants can be reported as either daily totals or as part of the FTE. Residential occupancy should be estimated based on the number and size of units. Core and Shell projects should refer to the default occupancy table in the Reference Guide appendix. All occupant assumptions must be consistent across all credits in all categories.) occupants.
Generally, the easiest and cheapest way to achieve this credit is to install low-flow and waterless fixtures. Using waterless urinals or pint-per-flush urinals in combination with ultra-low-flow toilets (1.0 gpf) or aggressive, dual-flushA type of water-saving toilet that gives a choice of flushes depending on the type of waste solid or liquid. toilets (1.28/0.8 gpf) can work, although it depends on your project occupancy and will need to be verified for each project.
If your project comes up just a little short, consider supplementing some of your potable water use with graywater or rainwater, or installing composting toiletsComposting (or Nonwater) toilet systems are dry plumbing fixtures and fittings that contain and treat human waste via microbiological processes..
Onsite wastewater treatment has a number of environmental and educational benefits, but treating to tertiary standards can be challenging for some projects, especially if they have limited space. The Solaire, a LEED Gold market-rate apartment building in Battery Park City in Manhattan, located wastewater treatment facilities in the basement because above-grade space was at a premium.
Treating to tertiary standards involves extra filtration or biological activity to remove nutrient pollutants such as nitrogen and phosphorus, and it may also involve disinfection. Treating wastewater to this level goes beyond code in most places. Consider technologies that are passive or low-tech in order to minimize operation and maintenance costs.
Once the wastewater has been treated to tertiary standards, you’ll need to determine the best reuse method. Many projects prefer to use it landscape irrigation. This will generally be your cheapest and easiest reuse method. If your project doesn’t have landscaping, consider reusing the treated wastewater for toilet flushing.
Office—In order for office spaces or other buildings to meet the credit through fixtures alone, they will most likely need to include waterless urinals. (Depending on your project, one-pint-flush urinals may work.)
Multifamily and Hotel—Residential and hotel projects, which don’t have urinals in private bathrooms, cannot meet this credit with low-flush fixtures alone, so they have to provide nonpotable waterNonpotable water: does not meet EPA's drinking water quality standards and is not approved for human consumption by the state or local authorities having jurisdiction. Water that is unsafe or unpalatable to drink because it contains pollutants, contaminants, minerals, or infective agents. or treat wastewater on site to earn the credit.
Check for local or state incentives for water conservation, which can make this credit more feasible. Rebates are common. Also, some municipalities offer treated wastewater to buildings, which may be used for toilet flushing (although in most places it is restricted to landscape use).
Perform a water-balance study for the entire project in order to make an informed decision about where to focus your water-saving efforts. Survey your project and site for all water sources—stormwater, graywater, and onsite wastewater.
Calculating irrigation water use is not required for this credit; however, understanding how indoor water use compares to outdoor water use can help you gauge where to focus your reduction efforts for the greatest benefit. Some water-saving strategies address both indoor and outdoor water needs holistically. For example, if you treat your wastewater onsite, you can use the treated water to irrigate your landscape as well as to flush toilets. Doing so can contribute to either WEc1: Water Efficient Landscaping and WEc3: Water Use Reduction.
Establish goals for indoor and outdoor water and wastewater reduction. You may want to include those goals in the Owner’s Project Requirements for EAp1: Fundamental Commissioning and EAc3: Enhanced Commissioning.
Consider reducing potable wastewater use by 100%, or treating 100% of your wastewater onsite to tertiary standards, for an Exemplary Performance point.
Determine which option is best for your project:
Some municipalities requiring rainwater capture to reduce stormwater runoff; if this is the case in your area, consider reusing the rainwater for toilet flushing.
Reusing graywater or rainwater incurs additional costs and requires dual plumbing. If you use an under-sink graywater system that shunts the water directly from the sink to the toilet, this also involves additional cost but may be less expensive than a centralized, dual-plumbed system.
Onsite wastewater treatment costs vary widely. Treating to tertiary standards, as required by this credit, can cost significantly more than treating to secondary standards.
Determine if composting toilets or waterless urinals are appropriate for your project. While not common, waterless fixtures can go a long way toward achieving this credit. Composting toilets do affect programming and layout, however, so be sure to consider them early in the planning stages. However, projects often find that installing only a few composting toilets can help them to achieve this credit while offering a great educational asset.
Check with the local municipal wastewater department to see if reclaimed water is available as a source of non-potable water for toilet flushing. If it is available, this will contribute to compliance with Option 1.
Check for codes that may limit your options or force you to obtain a variance. Plumbing codes often restrict or regulate the following water-saving technologies:
Determine your project’s baseline case wastewater generation. This will help you develop your strategy for reduction.
Reducing your shower or sink flow rate will not help with credit compliance for WEc2 but, will help with WEp1 and WEc3. However, if your project is earning this credit through treating wastewater onsite, it is best to reduce the total quantity of water being treated. Therefore, a reduction in flow fixtures will minimize the total water needing treatment.
Begin developing your strategy for wastewater use reduction based on the option you’ve selected. Research low-flush fixtures, water reuse, and onsite treatment.
Well and pond water are not considered non-potable water for the purposes of this credit and must count as potable water—so you won’t get credit for substituting them for conventional water sources. Water types that do count as non-potable are: graywater (lavatory, sink, and shower water), rainwater, treated wastewater, air-conditioner condensate, reverse-osmosis reject, and sump-pump water.
Consider monitoring wastewater reduction in conjunction with EAc5: Measurement and Verification.
Consider installing permanent water metering for ongoing monitoring of the project’s water use. A submetering system can help operations staff detect problems early and facilitate future LEED-EBOM certification.
Select water-efficient flush fixtures and determine the percentage of reduction from fixtures alone.
Consider the different maintenance requirements for waterless fixtures. Waterless urinals and composting toilets require a different maintenance program from conventional fixtures.
Remember that this credit is based on EPAct 1992.
Track and record information on applicable fixtures, including the manufacturer, model number, and flush or flow rate. This will help you when filling out the LEED Submittal Template. Fill out the Submittal Template calculator early in design simply as a draft to determine if you are meeting the requirement.
Typically, a dual-flush toilet—with the heavy-flow at 1.6 GPF and low-flow at 0.8 GPF—does not meet the credit requirements. However, a 1.0 GPF ultra-low-flow toilet or a 1.28/0.8 GPF dual-flush toilet—in conjunction with waterless or pint urinals—will meet the credit requirements, and you can avoid using non-potable water. For occupancies that do not use urinals, such as residences or hotels, you will not be able to meet this credit through the use of fixtures alone and you’ll find that you have to include non-potable water reuse in your water reduction strategy.
If you cannot meet the credit through the use of fixtures alone, determine how much non-potable water you need to use in order to comply.
Review your water balance study and determine what water reuse would be most appropriate for your project. If the building is residential or a hotel, it might be best to treat and reuse graywater from laundry or shower facilities. If the building is located in a rainy climate, you can capture and reuse rainwater.
If needed, size graywater and rainwater systems to satisfy the credit requirements. Sizing these systems can be more complicated than you might initially think. It’s best to involve a civil engineer or someone familiar with these systems.
Untreated rainwater and graywater may corrode plumbing systems or lead to biological growth. You should plan for water treatment and filtration, or use corrosion-resistant materials. All graywater plumbing and storage must be separate from regular sewage plumbing.
If you will be using graywater, rainwater, or treated wastewater, you’ll need dual plumbing for interior water fixtures. Communicate this need to your civil and plumbing engineers. You should also discuss any location and structural issues if your project is going to have a rainwater cistern—sometimes they take up more space than anticipated.
A dual plumbing system and rainwater or graywater reuse are likely to add upfront costs but the owner may recoup some of that cost in reduced water and sewer charges. However, most current utility rates for water and sewer are too low to justify these systems on a cost basis alone.
Typically, dual-flush and composting toilets have a higher cost over conventional fixtures but reduce water charges. Some ultra-low-flow toilets have a cost premium as well, but it is typically not as significant as a dual-flush or composting toilet.
Compare the baseline and design case water budgets to determine the water reduction percentage for your project. The LEED Submittal Template has a built-in calculator to facilitate this calculation. Repeat this process until selection of water fixtures and strategies is finalized and your project’s water reduction goals have been met.
Even if you are attempting Option 2, you will want to select water-efficient fixtures, which minimize the quantity of wastewater treated onsite. To accomplish this, target the most consumptive fixtures to achieve the greatest water reduction, but keep in mind the very different maintenance requirements for waterless fixtures. See WEc3: Water Use Reduction for more information. Also, review the Option 1 steps of this credit.
Determine what type of onsite wastewater treatment is most appropriate for your project. Typical septic-tank-and-leachfield systems used in many rural areas where there are no sewer systems do not treat water to tertiary standards so they can’t be used to earn this credit.
Verify that your onsite wastewater treatment system is capable of treating the wastewater to tertiary standards. State governments determine exactly what constitutes “tertiary treatment” based on allowable remaining levels of certain nutrients and organisms. Your civil engineer will need to be in charge of this determination.
Determine how treated wastewater will be used onsite. It must either be reused, such as for toilet flushing or irrigation, or must be infiltrated onsite.
Treating wastewater simply for sewage conveyance can be expensive, so make the most of tertiary-treated wastewater by using it for as many non-potable water applications as possible—irrigation, toilet flushing, and cooling tower makeup water.
While the capital cost of wastewater treatment is a significant deciding factor, seek technologies or strategies that have low maintenance requirements to keep operations and maintenance costs low. Alarm systems for malfunctioning wastewater treatment systems can be expensive, be sure to research this.
Depending on the technology used and state or local regulations, tertiary wastewater treatment may require contracting with an outside company for operations and maintenance. When researching treatment technologies, inquire about maintenance procedures and requirements.
Include any low-flow or waterless fixtures, water reuse systems, or onsite wastewater treatment systems in your construction and design development documentation.
Be certain that the contractors reviewing construction documents understand the purpose of any dual-plumbing system in the plans. Misunderstandings about plumbing can lead to costly and unsanitary mistakes—like cross-connection with potable water lines.
Consider including signage for water reduction strategies that may require special instructions for use. These may include: occupant signage for operating dual-flush toilets, waterless urinals and composting toilets, and for indicating non-potable water—and operational signage for distinguishing the pipes that carry reused water. Purple piping is commonly used for reclaimed water and, more recently, for recycled graywater.
If reusing graywater or rainwater, or treating wastewater onsite, ensure that the key system components, such as treatment and collection facilities, are not eliminated during value engineering.
Fill out the LEED Submittal Template. You will need to provide information on annual reused water amount and, and if necessary, plumbing drawings or calculations illustrating that your non-potable water systems are capable of supporting the quantities determined.
Fill out the LEED Submittal Template. You will need to provide information on the blackwater source (toilet or urinal), annual quantity treated, annual quantity infiltrated onsite, annual quantity reused onsite, and plumbing drawings or other documents that detail information about the onsite treatment, infiltration, and reuse capabilities of your project.
Be sure you’ve included startup of a wastewater treatment system in contract documents and scope of services. You may want the commissioning agent to look at the wastewater treatment system too.
The contractor needs to verify that the correct fixtures have been purchased and that applicable water reuse or treatment systems have been installed properly.
Be sure to use purple pipes or otherwise clearly label supply pipes carrying non-potable water. This practice avoids inadvertent cross-connection with potable water lines and provides educational value.
When using an innovative wastewater treatment system unfamiliar to local regulatory officials, include them in regular construction inspections. This often helps to ease acceptance, and avoid unexpected objections or problems.
Apply for water-reduction incentives and rebates through your municipal water authorities.
Provide building managers with manuals for all water fixtures, water reuse technologies, onsite water treatment systems, and unconventional products used.
If a submetering or ongoing monitoring system is in place, be sure to track and record monthly use. This can help detect problems, contribute to a comprehensive M&V plan, and help with LEED-EBOM certification.
Train cleaning and operations staff to maintain atypical fixtures such as waterless urinals, composting toilets, and graywater collection and rainwater catchment systems.
Some wastewater treatment systems require trained personnel to operate them.
Excerpted from LEED for New Construction and Major Renovations Version 2.2
Reduce the generation of wastewater and potable waterPotable water meets or exceeds EPA's drinking water quality standards and is approved for human consumption by the state or local authorities having jurisdiction; it may be supplied from wells or municipal water systems. demand, while increasing the local aquifer recharge.
Reduce potable waterPotable water meets or exceeds EPA's drinking water quality standards and is approved for human consumption by the state or local authorities having jurisdiction; it may be supplied from wells or municipal water systems. use for building sewage conveyance by 50% through the use of water-conserving fixtures (water closets, urinals) or non-potable water (captured rainwater, recycled greywater, and on-site or municipally treated wastewater).
Treat 50% of wastewater on-site to tertiary standards. Treated water must be infiltrated or used on-site.
Specify high-efficiency fixtures and dry fixtures such as composting toilet systems and non-water using urinals to reduce wastewater volumes. Consider reusing stormwater or greywater for sewage conveyance or on-site wastewa- ter treatment systems (mechanical and/or natural). Options for on-site wastewater treatment include packaged biological nutrient removal systems, constructed wetlands, and high-efficiency filtration systems.
This website offers a plumber’s perspective on many of the major toilets used in commercial and residential applications.
This site provides two reports on independent test results for a variety of toilets’ flush performance and reliability.
ARCSA was founded to promote rainwater catchment systems in the United States. The ARCSA website provides regional resources, suppliers, and membership information, and publications such as the Texas Guide to Rainwater Harvesting.
This manual provides a focused and performance-based approach to on-site wastewater treatment and system management. It also includes information on a variety of on-site sewage treatment options.
WaterSense is a U.S. Environmental Protection Agency program designed to encourage water efficiency in the United States through the use of a special label on consumer products. It was launched in 2006. The WaterSense website offers information on certified products, and other water conservation information from its partners.
The LEED Online credit form offers a useful calculator for this credit that we recommend. The scenarios shown in these sample calculations show how this credit can play out with percentage savings based on fixture selection alone.
This template is the flattened, public version of the dynamic template for this credit that is used within LEED-Online v2 by registered project teams. This and other public versions of LEED credit templates come from the USGBC website, and are posted on LEEDuser with USGBC's permission. You'll need to fill out the live version of this template on LEED Online to document this credit.
Documentation for this credit can be part of a Design Phase submittal.
WE 2.2 states, "minimize the amount of wastewater conveyed to the municipal system"
Can we automatically acheive this Credit by using an onsite Well and Septic system?
David, no, that is not sufficient. There is more explanation of treatment standards in the Bird's Eye View tab on LEEDuser, above.
I am finding it hard to locate a 1.0 or a dual flush 1.6/.8 toilet and flushometerA device that utilizes pressure from the water supply system, rather than the force of gravity, to discharge water into the bowl of a toilet or urinal. It is designed to use less water than conventional flush toilets.. Where did the data come from in the sample calculations? Lyn
Check the GreenSpec products list in the sidebar to the right. I think that's where we found it.
We are desiging a building with both a green roof and a rainwater harvest system. In the past we have used 75% collection efficiency for Equation 4 (Rainwater Volume) when the roof was metal. Obviously, the green roof will be absorbing more of the rainwater but I am wondering how much it would impact the percentage of efficiency. Does anyone know what percentage I should use for my calculation?
There is so much variation in green roof design—I doubt that a single reference figure would necessarily have any relevance. Climate and storm frequency is also highly relevant—if the growing medium is saturated by one storm, how quickly does the next storm come along? It might have 100% runoff if it comes quickly.
I would consult with your landscape architect.
Learning from our experience, I suggest you simply calculate the rain water harvesting potential using the run-off co-efficient of 0.3 (30%) to 0.1(10%) depending on the thickness of the green roof. So the final calculation will be area (mts) * Avg annual rainfall (mm) * co-efficient for surface run off.
While Tristan has made a valid point above you will find that there are some mild rainy days where the run off is zero and there are some days where the storm is continuous hence the run off can be up to 95% . So looking at rain water harvesting potential annually the values I have provided above are reasonably accurate as it balances out by the end of the year. This has been tested by us here in India.
Green Roof 100 mm - 200 mm = 0.30 run off co-efficient
Green Roof >= 500 mm = 0.10 run off co-efficient
Hope this helps.
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