Indoor Water Use

Engineering Inputs

Patrick Chopson avatar
Written by Patrick Chopson
Updated over a week ago

Inputs for Indoor Water Use are:

  1. Baseline Flow Rate: the assumed water consumption rate of code-compliant fixtures and fittings.

  2. Low Flow Rate: a reduced water consumption rate based on the selection of low-flow fixtures. Typically, a low-flow fixture will reduce water consumption by at least 20% when compared to conventional fixtures. The EPA WaterSense group has published a table (below, units in gal/flush) of Typical Flow Rates for each primary indoor water use fixture.

Indoor Water Use Fixtures: Permanently installed plumbing fixtures with running water.

  1. Toilets: a sanitary plumbing fixture used for human waster removal. Also known as a water closet.

  2. Urinals: a sanitary plumbing fixture for urination only.

  3. Showers: a plumbing fixture used for bathing.

  4. Kitchens: plumbing fixture used in common spaces. Includes kitchen sinks and drinking fountains. Exclude faucets used exclusively for filling operation, i.e. Janitorial faucets.

  5. Lavatories: plumbing fixture used in bathrooms. Also, know as a washbowl or basin. Includes both public and private bathrooms.

  6. Greywater (%): untreated wastewater which has not come into contact with toilet waste. Greywater is considered not suitable for human consumption, but can be treated to be used as a substitute water source for laundry equipment, toilet flushing, and outdoor use (irrigation).

  7. Fixtures not included in the Indoor Water Use Tool:
    - Clothes washers
    - Dish Washers (standard or compact)
    - Pre-rinse Spray Valves
    - Ice Machines
    - Utility sinks

Calculation Method and Results

The Indoor Water Use calculation method follows (BD+C) LEED v4.0 WE p2,c2 - Indoor Water Use Reduction credit, and AIA's COTE TopTen Toolkit: Measure 4 - Design for Water tool, section 1 - Indoor Water Use.
The four indoor water use related results are Indoor Reduction, Indoor LEED Points, Indoor WUI, Indoor Water Use by Building Type, and Indoor Water Use Breakdown bar graph. The difference between baseline fixture flow rates and low flow rates determine indoor water use reduction. The LEED rating systems for indoor water use reduction is on a 1 to 6 point scale and based on a %reduction threshold (table below).

WUI, or Water Use Intensity, is the number of gallons by building area required used for daily operations. Water Use by Building type is the amount of water, measured in gallons per year, used for each building template. Mixed-use projects will have multiple building types inside a single project, so cove.tool will explain how much water is being used for each section. Last, cove.tool graphs annual indoor water use by a fixture in the breakdown bar graph. This is calculated by occupant density to determine the number of fixtures, days of operation by using user-defined schedules, and user determined fixture flow rates. Note that Duration of Use and Uses per Day is taken from "LEED v4.0 - WE p2, Table 8 &9: Nonresidential and Residential default fixture uses" and the default gender ratio is 50:50.


Q1. Can I use cove.tool's water tool for LEED points?
> Yes! It can be used for Integrative Process Credit and understanding how many anticipated points can be achieved by building design, but LEED requires a more detailed tracking tool for credit compliance. This water tool is for planning and concept testing. Our intention is to get this to the compliance level in subsequent updates. Stay tuned! To pursue the Leed v4 p2, c2 Indoor Water use reduction credit users can use their values form cove.tool and enter them into the LEED's Indoor Water Use Reduction Calculator.

Q2. Where do I input the number of fixtures?
>You don't. Indoor Water Use is the measurement of water use according to fixture consumption rates and estimated use. In traditional plumbing design, calculations are based on fixture counts. This methodology calculates full-time-equivalent (FTE) and transient occupants’ estimated use per day and applying appropriate fixture use rates to each. The calculator estimates the percentage reduction of potable water use, compared with the baseline, using the following equation (from LEED v4 BD+C Reference Guide; WE p2: Indoor Water Use Reduction - Equation 1).

Using your occupant density input from the baseline page, cove.tool calculate the FTE and Visitors for your building type. For this, cove.tool uses the table below to calculate uses per day and duration. (From LEED v4 BD+C Reference Guide; WE p2: Indoor Water Use Reduction - Table 8)

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