California Water Use Legislation

California is experiencing large swings between drought and flood. In an effort to improve the State’s water future, legislation was passed to make conservation a California way of life. The State wants our water resources to be put to their fullest beneficial use. They want to ensure that the waste of water is prevented and the conservation of water is carried out in the best interest of the public welfare.

The resulting legislation created a framework that calculates a water budget for each water agency that is measured in the following categories:

  • Residential indoor uses
  • Residential outdoor uses
  • Commercial and Institutional outdoor uses
  • Water loss

Residential Indoor Use

The residential indoor standard was initially set at 55 gallons per person per day. That goal is scheduled to decline to 47 gallons per person per day in 2025 and 42 gallons per person per day by 2030.

To calculate each agency’s residential indoor water budget, census data is used to determine the number of people within an agency’s service area. That number is multiplied by the gallons per day objective above.  The State Water Board provided the schematic below to illustrate the Residential Indoor Budget calculation.
CA Leg Budget Calc

Residential Outdoor Use

The State wants to ensure that water for residential irrigation is used efficiently by applying a Landscape Efficiency Factor to each agency’s water budget. This factor is applied to the amount of water necessary to maintain healthy and efficient landscapes. This factor starts at 80% efficiency which means the efficiency of the irrigation system will require 20% less water. The efficiency factor will be reduced to 63% in 2030 and 55% in 2035. This assumes that irrigation will become more efficient in the future.

Evapotranspiration is also considered when calculating an agency’s outdoor water budget. Evapotranspiration is the rate at which water evaporates from the ground and transpires from plants. Each geographic area has a different evapotranspiration rate. The Lake Arrowhead area’s evapotranspiration rate is monitored by a Cimis station located at the Lake Arrowhead Country Club. Effective precipitation is then deducted from the evapotranspiration rate to get the net evapotranspiration or ETo.

To determine LACSD’s landscape area, LIDAR imagery was obtained by the State for each parcel, which broke down the square footage of each lot into the following categories:

  • Hardscaped or developed with a structure, non-irrigable
  • Land that is suitable for irrigation and is irrigated
  • Land that is suitable for irrigation but is not irrigated
  • Undeveloped land or natural area that is unlikely to be irrigated in the future

Each agency is given an allowance to efficiently irrigate the area that is currently being irrigated and 20% for the land that is suitable for irrigation but is not currently irrigated. This percentage may change in the future. There is no water budget given for undeveloped land or natural area.

All of this data is then multiplied by a unit conversion factor of 0.62 (gallons per square feet times inches) to arrive at LACSD’s annual water budget for residential outdoor uses. Below is a graphic provided by the State Water Board that illustrates the calculation.

Commercial and Institutional Outdoor Use

Commercial and Institutional outdoor water use targets are calculated in the same manner as the residential outdoor use as specified above but the 2035 Landscape Efficiency Factor will be set at 45%. In certain circumstances, a water meter that is solely monitoring irrigation may need to be installed. Land that is irrigated with recycled water is not included in this calculation.
CA Leg Outdoor

LACSD is also required to categorize all of its commercial and institutional customers into certain classifications. Water usage will be reported by the various classifications and certain applicable best management practices will be recommended.

Water Loss

Real water losses occur from leaks in the water distribution system. In 2022, the California State Water Board established a standard for each individual water agency. LACSD has taken proactive steps to reduce leaks from our system. Results of these efforts are documented in annual American Water Works Association water audits.


These water use objectives may also include variances for unique situations that can have a material effect on an agency’s goals. LACSD qualifies for a variance related to seasonal populations.

Residential indoor use as calculated above utilizes the census to determine the population, but in Lake Arrowhead, many of the residential homes are occupied by short-term renters or seasonal home owners who claim a different residence in the census. A water use model has been developed to try to estimate the number of full-time vs. part-time residences.