Tools & Calculators

Water Budgeting

As an irrigation management tool

  • A water budget is a water management tool used to estimate the amount of water a landscape will require. It can be calculated for a single irrigation event, on a weekly or monthly basis, or even annually.
  • The water budget takes into account reference evapotranspiration data, plant type(s), purpose and functionality of the landscape, irrigated landscape area, irrigation efficiency, water quality, and rainfall.
  • For additional information on how to create a water budget, refer to Landscape Irrigation Best Management Practices, appendix B.

As a landscape design tool

  • The concept of water budgeting can also be used as a landscape design tool, especially when water resources may be limited. The availability of water influences the size and type of plantings that will be compatible with water availability.

Examples of water budgeting tools that influence the landscape design include the following:

  • The EPA WaterSense Water Budgeting Tool calculates a water allowance based upon a percentage of reference evapotranspiration (ET). The landscape water requirement is then compared to the allowance. If the water requirement exceeds the allowance, then changes to the landscape are made so that the estimated landscape water requirement is less than the water allowance.

Other programs that utilize the EPA water budgeting tool include Sustainable Sites Initiative Version 2 and United States Green Building Council’s LEED Version 4 program.

  • The California Model Water Efficient Landscape Ordinance (MWELO) is a mandatory requirement for all new buildings, both residential and nonresidential, as part of their building code. The link will allow you to read the ordinance and access water budget calculators so that the landscape design will comply with the requirements of the ordinance.
  • The Florida Water Star program likewise uses a water budget calculator to determine the amount of water required by the landscape on a per irrigation zone bases. The Florida Water Star water budget tool considers the irrigation schedule, as well as the plant materials and irrigation type. The estimated amount of water that will be applied through the year must be less than 12.5 gallons, or 20.0 inches per square foot. 

Water Budgeting Resources