How are commercial water budgets calculated?

There are two types of commercial water budgets: 

  • Mixed-use accounts for customers that only use water indoors or may have both indoor and outdoor water use on the same meter
  • Dedicated irrigation accounts that only use water for landscape irrigation

Mixed-use Accounts

Water budgets for mixed-use accounts are calculated based on an average of their past use for each month. For new mixed-use accounts, a monthly average is calculated following the first full year’s water use.

Dedicated Irrigation Accounts

Water budgets for dedicated irrigation accounts are calculated using three factors:

  • Irrigated landscape area
  • Daily localized weather data
  • Landscape factor

For example, a dedicated irrigation account with 43,560 square feet if irrigated landscape area and an ET for May of 5.72 inches the outdoor water budget would be:

43,560 x 5.72 x 0.8 x .62 = 123,585 gallons of water / 748 gallons =165 billing units

Irrigated landscape area

The irrigated landscape area is the amount of landscaped area on your property that receives regular watering. Western may use Riverside County Assessor parcel data or its geographic information system (GIS) to determine the default irrigated area for your home.

Localized weather data (Evapotranspiration or ET)

The amount of water that is lost each day from your landscaping due to evaporation and plant transpiration is known as evapotranspiration (ET), and it varies daily due to factors such as wind, humidity and temperature. Western measures ET daily using a system that calculates precise weather data for more than 460 distinct microclimate zones within our retail service area. ET values change with the weather, so the water budget for landscapes is larger in hot weather and smaller in cooler weather.

Landscape factor

The landscape factor measures the specific amount of irrigation water required by your landscape. Water services installed in Western’s retail service area on or before December 31, 2011, are given a landscape factor of 0.8, which is sufficient if your landscaping is mostly grass with a mix of shrubs or flowers. Water services installed on or after January 1, 2012, are given a landscape factor of 0.7 because new construction is required to use the latest water-efficient irrigation systems.

Landscape sites that qualify under the 2010 State Model Landscape Ordinance as a “special landscape” are given a landscape factor of 1.0. It is the account holder’s responsibility to notify Western if a site qualifies for “special landscape” considerations. The special landscape factor is applied at Western's discretion.

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