WELO Water Budget Based Landscape Design Tool

Urban Farmer Store customers can benefit from tools that help them upgrade their landscapes to meet water efficiency and sustainability standards. The tool helps designers of residential landscapes conceptualize and design based on the water budget approach and the most recent water efficiency standards. It is structured using the Water Efficient Landscape Worksheet (Appendix B) from California’s updated Model Water Efficient Landscape Ordinance (MWELO). This tool was developed by Urban Farmer Emeritus Tom Stewart in his retirement who generously shares it with us.

The WELO Water Budget Tool Instructions for Use

This tool was formatted using Microsoft Excel by Tom Stewart.

Download (XLSX, 54KB)

Also can be utilized with Google Sheets.

Data Entry

Data entry is simple with few data entry points.

  1. Enter a sample from the ETo’s listed or refer to MWELO’s Appendix A, CIMIS, etc.
  2. Identify specific design hydrozones from the preselected list that generally fit site design needs.
  3. For Regular Landscape Area, enter irrigation type (1 for spray, 2 for drip) for each selected hydrozone. Do not enter irrigation type for water features.
  4. For Regular Landscape Area, enter the number of square feet for each selected hydrozone. Enter the water surface area for water features.
  5. For Special Landscape Area, enter the number of square feet for each selected hydrozone.
  6. Observe and adjust results as needed.


The Water Budget Calculator must show that:

  1. The value in the Total Landscape Area box equals the site landscape area as defined by Landscape Area in the definitions below;
  2. The value in the ETWU box does not exceed the value shown in the MAWA box; and
  3. The value in the ETAF box does not exceed 0.55.


The calculator ‘s plant factor settings are selected from the ranges described in MWELO: high water use equals 0.8; moderate water use equals 0.5; low water use equals 0.2; very low water use equals 0.09; and water feature equals 1.0. All other settings used are those also prescribed by MWELO.

Features and benefits

The tool is graphically understandable, easy to use, and features minimum data entry requirements. It introduces users to important water efficiency concepts such as water budget, hydrozone, evapotranspiration, water conserving difference between drip and spray irrigation, and landscape water use efficiency as defined by MWELO. It can help users conceptualize and understand water efficient landscapes based on a water budgets, and use it as a planning and design assistant for converting their landscapes to meet current water efficiency standards.


This version of the Water Budget Based Landscape design tool is not formatted for application to commercial landscapes (ETAF = 0.45) or existing non-rehabilitated landscapes (ETAF = 0.80). Plant factors are set at mid range values and can’t be adjusted to account for modified site factors such as microclimate and plant density. It does not include an option for effective precipitation as it strictly follows the format shown in the 2015 MWELO Appendix B. The tool provides residential customers with a convenient vehicle for helping them visualize and design their water efficient landscapes. It is not meant for use by professionals for the purpose of fulfilling certification requirements.


Definitions are listed for terms and labels found in MWELO Appendix B and the Water Budget Based Landscape Design Tool. Additional definitions can be found in the definitions section of DWR’s MWELO document.

(1) Maximum Applied Water Allowance (MAWA) is the baseline volume (in gallons) of water allowed for annual application to a landscape:

(2) Estimated Total Water Use (ETWU) tests the landscape design for assurance that the annual gallons required for its irrigation remains below MAWA.

(3) Evapotranspiration Adjustment Factor (ETAF). When applied to reference evapotranspiration ETAF adjusts for plant factors and irrigation efficiency. For residential areas, this tool applies the ETAF factor of 0.55 to regular landscape areas and 1.0 to special landscape areas (see below) of residential landscapes.

(4) Landscape Area means all the planting areas, turf areas, and water features in a landscape design plan subject to the MAWA calculation. The landscape area does not include footprints of buildings or structures, sidewalks, driveways, parking lots, decks, patios, gravel or stone walks, other pervious on non-pervious hardscapes, and other non-irrigated areas designated for non-development (e.g., open spaces and existing native vegetation).

(5) Regular Landscape Area is the landscape area covered with landscape plants to be irrigated and for which ETAF for hydrozones is calculated with the formula ETAF = PF/IE. It also includes the water surface area of water features, excluding water features using recycled water.

(6) Special Landscape Area (SLA) means an area of the landscape dedicated solely to edible plants, recreational areas, areas irrigated with recycled water, or water features using recycled water. The ETAF = 1 for SLA hydrozones.

Historical Reference ET by City from WELO Appendix A

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