Tiered Rates and Water Budgets

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The City implemented tiered water rates to promote efficient water use, establish fair rates, and promote conservation of this precious resource.

The City of Corona Department of Water and Power implemented a tiered rate and water budget system in April, 2010. Tiered rates and water budgets are effective at promoting efficient water use and resource conservation. They provide enough water for typical but efficient water use indoors and outdoors. Tiered rates also provide a means to charge fair rates based on how water is being used. Inefficient water users will pay a higher cost for water than efficient water users.


How Your Water Budget Was Determined

Commercial customer budgets are based on a three year historical average of water use. 

Residential customers have an indoor and an outdoor budget. The calculation looks like this: 

  • Indoor Budget = number of people x 60 gallons/person/day x number of days in the billing period
  • Outdoor Budget = Irrigated Area x ET x PF/IE

Haven't been in business for 3 years?
The first year of water service is at the Budget rate. For the second year of service, the water budget is based on your usage during the first year. Questions? Contact Customer Care at (951) 736-2321 for more information on your budget calculations.


About the Indoor Budget

Your indoor budget is based on the number of people in your home. Each person is budgeted 60 gallons of water per day for each day in the billing period.


The American Water Works Association's (AWWA) 1997 study showed that on average, a person uses about 60 gallons of water each day indoors. The flows that come into the City's treatment plants confirmed that 60 gallons of water per day per person is accurate for Corona residents.

The number of residents in each home is based on the 2000 census that indicated Corona has an average of 3.4 residents per single-family residence. The City has chosen to use 4 as the standard.

About the Outdoor Budget

Your outdoor budget is the irrigated area, times the Evapotranspiration (ET) factor, times the Plant Factor (PF), divided by Irrigation Efficiency (IE). 

Commercial Customers
The outdoor budget depends on the type of account you have:
- Structure or Mixed-Use Meter: Budgets are based on a three-year rolling average of historic water use. 
- Dedicated Landscape or Reclaimed Meter: Outdoor budget =Irrigated Area x ETx PF/IE

Residential Customers
All residential customers have an indoor and an outdoor budget. The calculation looks like this: Irrigated Area x ETx PF/IE

  • Evapotranspiration Factor (ET) = evapotranspiration which is the amount of water lost by soil evaporation and plant transpiration each day.
  • Plant Factor (PF) = the amount of irrigation water required (currently using a Plant Factor of 0.8).
  • Irrigation Efficiency (IE) = this factor accounts for inefficiencies in the irrigation system (currently using 0.7 efficiency). 

Here's what those terms mean

Irrigation efficiency indicates how efficiently your irrigation system operates. It is the measurement of the beneficial use of applied water to plants, and is measured against the total water that was applied. Ideally, all irrigation systems should be 100% efficient. In reality, most systems are not efficient and have water loss due to factors such as wind and runoff. A well designed irrigation system can have an irrigation efficiency factor of 0.8 to 0.9, while poor systems can have a factor of less than 0.5. Most systems have an irrigation efficiency factor ranging from 0.65 to 0.9. Your outdoor budget is calculated using an irrigation efficiency factor of 0.7.

The plant factor is the amount of irrigation water required by a plant. Plant factors vary by the type of plant. Plant factor is used to estimate the water needs for landscapes. For example, turf grasses have a plant factor between 0.6 and 0.8. Warm season turf grasses, such as Bermuda and St. Augustine have plant factors of 0.6. Cool season turf grasses, such as Fescue and Blue Grass have Plant Factors of 0.8. Water efficient plants may have a plant factor of 0.0 to 0.6. Your water budget will be calculated using a plant factor of 0.8, which is the amount of water needed by most turf grasses.

Evapotranspiration, or ET, is the amount of water that is lost each day due to evaporation and plant transpiration. Evaporation is water lost from the soil due to factors such as wind, humidity and temperature. Plant transpiration is the amount of water that plants lose from their leaves and plant tissues. Evapotranspiration is an indicator of how much water crops, lawns, gardens and trees need for healthy growth and productivity. By measuring evapotranspiration, only the amount of water that is lost will be put back into the soil, therefore reducing water waste. The evapotranspiration rate is measured on a daily basis, and is measured in inches. For your water budget, the ET for each day in the billing cycle is added up and used to calculate your outdoor budget. There is a higher evapotranspiration rate in the summer than in the winter, when the weather is warmer. Your budget will adjust each month to account for evapotranspiration, so your budget will be higher in the summer than in the winter. The ET data that Corona is using for the tiered rates comes from a CIMIS (California Irrigation Management Information System) weather station data located at UC Riverside. For more information on CIMIS, visit www.cimis.water.ca.gov.


Have Questions?

Need a Water Budget Variance? 
Click here
 to find the forms and information you need...

Wondering about water quality?

Click here to see the annual Consumer Confidence Reports....

Looking for ways to lower your water bill?
Check out our rebate and savings programs in the Conservation section.


Learn More

Water Budget Variance
Questions & Answers 
Water Rates
Water Use Profile

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