Water Budget Based Rates

Water Budget Based Rates in Detail


Designed to Meet Your Needs

Every MNWD customer receives a personalized water budget each month designed to meet their specific indoor and outdoor water needs, which means that no matter the size of your household or yard, you should be able to remain within your water budget and pay the lowest available price. Residential water budgets are calculated based on each customer’s landscaped area of their parcel, real-time localized weather data, and the number of residents in each home, among other factors. Residential water budgets vary from month-to-month based upon the weather and the number of billing days in each cycle. 

How to Calculate Your Water Budget 

Residential customers have both indoor and outdoor water budgets. The infographic below demonstrates how your water budget is calculated. To visualize how changes in your water use can affect your monthly bill, visit our interactive online bill calculator at www.mnwd.com/billcalc.


Indoor Water Budget

The indoor water budget is calculated using these three factors

  1. 60 gallons of water per person, per day
  2. The number of people in the household
  3. The number of days in the billing cycle

Average Amount of Water Used

A recent study showed that, on average, a person will use about 47 gallons of water each day indoors. This number includes all indoor water use, such as showers and washing clothes, and is based on water-efficient devices. MNWD utilizes a budget of 60 gallons per person per day. For comparison, other water agencies in Orange County have budgeted 50 to 60 gallons per day for each customer’s indoor use.

People Per Household

The most recent census data shows there is an average of 2.65 people per household in MNWD’s service area. Each single-family home receives a default number of four people per home. Condominiums receive a default of three people per home, and apartments have a default of two people. Customers are encouraged to contact the District if they have more than the default number of permanent residents, requiring a larger indoor water budget. A variance is available for customers with a greater number of people in their household.

Days in Billing Cycle

This is the number of days that you are being billed for service. This information can be located on your water bill, and comes from the meter read dates. It may differ from bill to bill, but will usually be between 28 and 35 days.

 Indoor Water Budget Formula

60 gallons per day x number of people x number of days on bill


  • 4 people in the household, 30-day billing cycle
  • 60 x 4 x 30 = 7,200 gallons of water/748 gallons = 9.6 billing units* (rounded up to 10 billing units)

*1 billing unit = 748 gallons

Outdoor Water Budget

The outdoor budget is calculated using three factors:

  1. Irrigable area per parcel
  2. Daily evapotranspiration
  3. Plant factor

Irrigable Area 

The irrigable area is the amount of landscaped area on the property that receives regular watering. Pools and spas are also included in the irrigable area. County Assessor parcel data and the District’s Geographic Information System were used to determine the irrigable area for your home.

Daily Evapotranspiration

Evapotranspiration (ET) is the amount of water that is lost each day due to evaporation and plant transpiration. Evaporation will vary 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. The ET rate is measured every day in inches. The actual ET corresponding to your microzone is added up for each day in the billing cycle to determine the monthly ET.  There is a higher ET rate in the summer when the weather is warmer, than in the winter. MNWD measures ET using 110 virtual weather stations that can calculate precise data for 110 distinct microclimate zones within our service area. Click here for a map of the 110 microclimate zones. 

A customer may go to www.cimis.water.ca.gov to obtain referential daily ET data by going to the “Data” tab, selecting “Station 75,” and then clicking the “Run Report” button in the lower right hand corner. This is to be used as reference only for the ET on the water bill, as the ET value may not exactly match the ET for a particular microclimate zone.

Historical ET data can also be useful as an indicator for gauging how outdoor water budgets can change from month to month. The historical average monthly ET is listed below. Please note that this is only for use as a reference, and actual ET can vary slightly based on actual weather and microzone.



Plant Factor

The plant factor measures the specific amount of irrigation water required by each type of plant in your yard. For example, turf grass has a plant factor between 0.6 and 0.8, while water-efficient plants may have a plant factor of only 0.3 or 0.4. Residential water budgets are calculated using a plant factor of 0.7.

Outdoor Water Budget Formula

Irrigated acreage x ET x plant factor x 0.62 (conversion factor from inches to gallons)


  • 5,000 square feet of irrigated acreage, ET of 5.72 inches
  • 5,000 x 5.72 x 0.7 x 0.62 = 12,412 gallons of water/748 gallons = 16.59 billing units* (rounded up to 17 billing units)

*1 billing unit = 748 gallons

Commercial Customers

Commercial water budgets are calculated based on a three-year rolling average of each commercial customer’s monthly use. If your business has landscape irrigation needs, an irrigation water budget is calculated based on the size of the landscaped area and real-time localized weather data, among other factors. If you have questions, please contact the Conservation Department at (949) 448-4025.

Recycled Water

Outdoor water budgets for recycled water accounts are calculated similarly to residential outdoor water budgets; however, the plant factor is slightly higher to accommodate more areas with turf.


Public Spaces

Outdoor water budgets for public spaces are calculated similarly to residential outdoor water budgets; however, given that most public spaces have more areas of turf, the plant factor is higher.


Water Budgets in Detail

Residential and Multi-Family Customers

For residential and multi-family customers, the rate structure for the consumption charge has five tiers. Residential customer who stay within their water budget remain in the first two tiers:

Tier 1: Indoor Water Budget

Tier 2: Outdoor Water Budget

Tier 3: 101% to 125% of Total Water Budget

Tier 4: 126% to 150% of Total Water Budget

Tier 5: Over 151% of Total Water Budget

Commercial Customers

For commercial customers, the rate structure for the Consumption Charge has four tiers. Commercial customers who stay within their water budget remain in the first tier:

Tier 1: Up to Total Water Budget*

Tier 2: 101% to 125% of Water Budget

Tier 3: 125% to 150% of Water Budget

Tier 4: Over 151% of Water Budget

*Total water budget is equal to the indoor water budget plus outdoor water budget for residential and multi-family customers, the outdoor water budget for potable irrigation and recycled customers, and three-year monthly average for commercial customers.

For information about water rates, click here.



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