How the inputs impact water use calculation

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

Irrigation, also known as outdoor water use, refers to the amount of water used to irrigate outdoor vegetation.

  1. Irrigated Area (ft²): amount of outdoor vegetated area that is supplied water regularly. Typically, this includes landscaped areas that are irrigated with or without an in-ground/automatic irrigation system along with areas regularly watered by hand. If you have vegetated areas that were specifically xeriscaped to require no water at all, these may be included in your total.

  2. Potable Water Irrigation: water that is of sufficient quality for human consumption. Typically obtained from public water systems that are classified, permitted, and approved for human consumption. Is potable water used for irrigation (after 2year establishment period)?
    - Yes
    - No

  3. Evapotranspiration (in): amount of water added to the atmosphere in standard conditions. In other words the measure of evaporation and plant transpiration from sources such as the soil, plants, trees, water bodies, landmasses and oceans as they are added to the air. Climates features like humidity, temperature.
    - Cool Humid: 3.8 in
    - Cool Dry: 5.3 in
    - Warm Humid: 5.3 in
    - Warm Dry: 6.8 in
    - Hot Humid: 8.3 in
    - Hot Dry: 12 in

  4. Plant Quality Factor (Qf): an adjustment factor for a plant's performance during optimal irrigation. In other words, what natural irrigation condition is most optimal? There is limited benefit in testing plants performance outside of baseline (0.8 Qf), but is available for cases in which changes to the climate are expected.
    - No Water Stress: 1 Qf, or a rainy season
    - Baseline: 0.8 Qf, or a typical season
    - Some Water Stress: 0.4 Qf, or a dry season

  5. Plant Factor (Pf): The relative amount of water that a plant requires, as compared to turf grass. Turf being the most standard and heavily irrigated vegetation type is a 1 Pf. All water intake required by other vegetation types will be measured in relation to common turf grass.
    - Turf: 1 Pf
    - Garden/Agriculture: 1 Pf
    - Annual Flowers: 0.8 Pf
    - Orchard/Evergreens: 0.8 Pf
    - Orchard/Deciduous: 0.7 PF
    - Perennial Flowers: 0.7 PF
    - Ground Covers: 0.6 PF
    - Trees: 0.6 PF
    - Shrubs: 0.6 PF
    - Native Plants: 0.2 PF

  6. Irrigation Efficiency: Water diffusing method. Each water diffusing strategy has a known efficiency rating based on the percentage of water used by the plants and water excess which becomes runoff or absorbed into the ground.
    - Drip: 0.9, or 90% of water is used by plant.
    - Sprinklers: 0.75, or 75% of water is used by plant.
    - Sprinklers, slope: 0.6, or 60% of water is used by plant.

Why is Outdoor Water Use Reduction Important?

Landscape irrigation practices consume large quantities of potable water, sometimes accounting for 30% to 70% of the water consumed in non-agricultural use. Good landscape design and use of native, adapted, and drought tolerant plants can dramatically reduce and even eliminate the need for irrigation while better integrating the building site into its surroundings and attracting native wildlife. Native plants also tend to require less fertilizer and fewer chemical pesticides, which degrade water quality when carried away in stormwater runoff.

Calculation Method and Results

The Irrigation/Outdoor Water Use calculation method follows AIA's COTE TopTen Toolkit: Measure 4 - Design for Water tool, section 1 - Predicted Water Use, and (BD+C) LEED v4.0 WE p1,c1 - Outdoor Water Use Reduction credit.
The three irrigation related results are Outdoor Reduction, Outdoor LEED Points and Total Irrigation Water Use. By default all projects begin with a baseline template for a turf-based irrigation setup. As users start to alter from the baseline assumptions and customize their outdoor water use plan, Total Irrigation Water Use will increase our decrease. The difference between a baseline turf-based irrigation plan and your custom plan will calculate the water use reduction. The LEED Rating systems for outdoor water calculation is simple: No irrigation or 100% outdoor water use reduction is 2 LEED points, and 1 point for 50% outdoor water use reduction.

Understanding the Monthly Irrigation Water Use bar graph

Cove.tool calculates monthly irrigation by first calculating annual total irrigation using the proposed irrigation plan and area, then multiplying by the standard monthly irrigation coefficients, as seen below.


1. Does the Monthly Water Use graph take into account frozen ground months, or other unique seasonal conditions which would cause ?
>No, some building locations will have unique seasonal conditions which cannot be predicted or known by the tool. In months where it is typical for the ground to be 100% frozen and absolutely no irrigation would take place, users can subtract the monthly gals/yr during the known frozen months from the final total to determine total irrigation.

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