Indoor water use reduction | U.S. Green Building Council
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LEED O+M: Existing Buildings | v4 - LEED v4

Indoor water use reduction

Required

Submittal Tips (click to expand)

WE Prerequisite: Indoor Water Use Reduction

Option 1. Calculated Water Use
  • Be sure the occupancy values have been used consistently throughout the application. Describe any justifiable differences in a narrative.
  • Use a 50/50 gender ratio in the calculations unless an alternate ratio is justified and will be valid for the life of the project.
  • Be sure the Percent of Occupants column in the calculations has been completed correctly. This column is intended to represent the percentage of occupants within each gender that have access to each fixture type. The calculations should list 100% if all occupants within each gender have access to each fixture type or should sum to 100% for each gender if there are multiple flush/flow rates for a particular fixture type.

    Note that it is recommended that the Resources page of this prerequisite in the Credit Library be checked for the newest version of the calculator.

  • Use a 50/50 gender ratio in the calculations unless an alternate ratio is justified and will be valid for the life of the project.
  • Multiple fixtures from one fixture family cannot be assigned to the same fixture usage group unless the values in the "Percent of Occupants" column for a given fixture family and gender sum to no more than 100%. When completing the calculations:

      Assign only one fixture from each fixture family to each fixture usage group. Fixture families include urinals, water closets, lavatory sinks, kitchen/break room sinks, etc. If multiple fixtures from within a fixture family are present, they should be represented in multiple fixture usage groups. List the Percent of Occupants as 100% for each fixture.
      OR

      Modify the Percent of Occupants values for the fixtures to accurately represent the percentage of occupants within each gender that have access to each [list affected fixture families] with a differing [flush/flow] rate. For example, if 50% of males have access to one urinal model and 50% of males have access to another urinal model, enter "50%" in the "Percent of Occupants" column for each urinal.

  • Don't forget to include kitchen and break room sinks available to building occupants. If occupants do not have access to these types of fixtures, include a narrative. Commercial kitchen (food service) sinks and prep sinks, including pot filling sinks, wash-down, and cleaning sinks may be excluded.
  • If unisex restrooms are present in the building, make sure the calculations have been adjusted accordingly. The value for "Percent of males expected to use restrooms with urinals" in the calculator can be modified as necessary to accurately identify the percentage of males who have access to or regularly use restrooms with urinals.
  • Ensure information is reported consistently - if the floor plans show unisex restrooms, ensure that the calculations include unisex restrooms. If the floor plans show unisex restrooms, but the building does not in fact have these in place (if the floor plans are outdated, for example), clarify the inconsistency with a narrative.

  • When categorizing lavatories as public or private, keep in mind that private use applies to those fixtures in residences, hotel or motel guest rooms, and private rooms in hospitals. All other applications are deemed to be public.
  • When calculating the average flush rate for dual flush water closets, use the averaging method described in Step 3 under Option 1 in the Step-by-Step Guidance section of this prerequisite in the LEED O+M v4 Reference Guide. The value for weighted average flush rate must be based on an assumption of two low flow flushes per person per day and one high flow flush per person per day, and it must account for the fact that males will use urinals (if present), not water closets, for the low flow flushes.

    The LEED v4 Indoor Water Use Calculator includes a built-in dual flush calculator.

  • If completely vacant spaces were present during the performance period, ensure the project has adhered to the guidance under the Variable Occupancy header in the Further Explanation section of this prerequisite in the LEED O+M v4 Reference Guide.
  • Non-potable water use does not count toward compliance with the prerequisite requirements. Non-potable water use can count towards additional savings in WEc Indoor Water Use Reduction.
  • For Retail, Hospitality, and Schools projects, the process and appliance water equipment purchasing policy should cover at minimum the purchase of products from Table 2 in the prerequisite requirements that are within the building and site management’s control.
Option 2: Metered Water Use
  • Verify that water systems serving at least 80% of the indoor plumbing fixtures and fittings are submetered. If not, the project must use Option 1.
  • If any vacant spaces were present during the performance period, be sure to identify the occupancy rates for the performance period and baseline period. If there was more vacant space during the performance period than the baseline period, demonstrate that the water use savings are not due to the decrease in occupancy.
International Water Labeling Programs Instructions

International Water Labeling Programs

How to Use USGBC's Indoor Water Use Reduction Calculator (O+M)

Water Use Reduction Case Study: Thurgood Marshall K-8 School