Water budgets are assigned to all Irrigation Classes to encourage appropriate water use during all seasons. They assign a water use target based on the size of a property’s irrigated landscape area and the evapotranspiration rate during each two month billing cycle. Water budgets are tied to a tiered rate structure that charges a higher rate for water use above the budgeted amount.
How Water Budgets Are Calculated
Each irrigation class water meter is assigned a water budget based on the irrigated landscape area served by that meter. Customers are responsible for providing Helix conservation staff with a map and/or description of the landscape area served by each meter.
Helix conservation staff calculate customer water budgets using the formula below, which complies with the Maximum Applied Water Allowance (MAWA) outlined in California’s Model Water Efficient Landscape Ordinance.
Water Budget in HCF = [LA x (ETAF x ETo) x 0.62] / 748
Irrigated landscape area (sf)
ET adjustment factor
- 0.7 for existing, non-rehabilitated landscapes
- 0.55 for residential landscapes, new or redeveloped, permitted on or after December 1, 2015
- 0.45 for non-residential landscapes, new or redeveloped, permitted on or after December 1, 2015
- 1.0 for schools or public sites with functional use turf (parks, picnic areas, athletic fields)
Reference evapotranspiration rate in inches from nearest CIMIS station (Escondido Station 153 or Otay Lake Station 147)
Converts inches to gallons per square foot
Converts gallons to hundred cubic foot units (1 HCF unit = 748 gallons)
About the ET Rate
- The California Irrigation Management Information System (CIMIS) lists historical and daily figures at www.cimis.water.ca.gov. Helix water budget calculations comply with CIMIS figures. When the water budget program began in 2009, historical ETo values were used. Effective November 16, 2015, daily ETo values will be used to calculate bi-monthly water budgets for each irrigation meter.
- Helix calculates water budgets for each two month billing cycle.
- Helix may modify the ET Adjustment Factor when water shortages occur.
If a customer believes that the assigned budget is too low given their site conditions, they may apply for a variance to their water budget for potential adjustments to the irrigated landscape area, plant type or other special circumstances approved by the General Manager or his/her designee.
Newly planted, water efficient landscapes (with a crop coefficient of less than 50%) are eligible to apply for an increased water budget during the establishment period, which is not to exceed three years. The watering schedule must be reduced to comply with the site’s standard water budget within three years. All requests are subject to field verification.
If Helix is unable to confirm the landscape area served by each meter, the District will assign a water budget of 1 unit/1 HCF per billing period per meter, until such time as the required information is provided and confirmed.