What is a water budget and how is it calculated?

The total water budget is based on number of people per household plus the estimated irrigated landscape area. This is divided into two tiers:

• Tier 1 – Low Volume
  • This is the first 20% of your total water budget.
• Tier 2 – Budgeted
  • This is the final 80% of your total water budget.

Customers may see their water budget for the current billing period, as well as a forecasted water budget for the next three months, on the left hand column of the billing statement.

What if I need more water than my budget gives me?

Customers may apply for a variance to their water budget to adjust the number of people in a household, irrigated area, or for a special circumstance such as a home daycare facility. Please click here for more information on EMWD’s variance process.

What if I think I’m going to go over my budget?

Customers may take advantage of a variety of programs and rebates such as a home water audit or rebates for indoor and outdoor water-efficient devices when available.

How much water is in a billing unit?

One billing unit is 748 gallons of water.

What is daily ET?

Daily ET is the amount of evapotranspiration (ET) that occurs on a daily basis in our service area. It measures – in inches of water per square foot, per day – what is lost to the atmosphere by the combined processes of evaporation (from soil and plant surfaces) and transpiration (from plant tissues). Many factors affect daily ET measurements such as solar radiation, air temperature, relative humidity, and wind speed.

What is CIMIS?

CIMIS is the California Irrigation Management Information System, a program of the Office of Water Use Efficiency (OWUE) within the California Department of Water Resources (DWR) that manages a network of more than 120 automated weather stations in the State of California. CIMIS was developed in 1982 by DWR and the University of California, Davis to assist irrigators in managing their water resources efficiently. Efficient use of water resources benefits Californians by saving water, energy, and money.

Where does EMWD get its ET data from?

EMWD obtains daily evapotranspiration (ET) data from the California Irrigation Management Information System (CIMIS).

Why is my ET value different from CIMIS data?

EMWD is using spatial CIMIS data. DWR gathers daily weather data (temperature, humidity, wind speed and rainfall) from CIMIS weather stations within and near the service area and then extrapolates that data into 50 different weather zones to accommodate for microclimates within EMWD’s 555 square-mile service area.

Where can I see my ET data?

At this time, daily ET data is not available for viewing by the customer. EMWD intends on making this data available sometime in the future.

How is ET data used to calculate my water budget?

The calculation is: BU = ET X CF X DF X LA X 0.62 X 0.001337

BU = Billing units allocated for your outdoor water budget (1 BU = 100 cubic feet)
ET = Sum of observed ET values for the billing period in inches
CF = Conservation Factor*
DF = Drought Factor**
LA = Landscape Area in square feet
0.62 = Conversion factor to convert inches per sq. ft into gallons per sq.ft.
0.001337 = Conversion factor to convert gallons into billing units.

*The Conservation Factor (CF) varies by account. Newer homes feature more water-efficient irrigation systems and are assigned their CF as follows:

• Connected prior to 9/1/2008: 0.8 CF
• Connected 9/1/2008 through 12/31/2010: 0.8 CF
• Connected 1/1/2011 through 5/31/2015: 0.7 CF
• Connected on or after 6/1/2015: 0.5 CF

**The Drought Factor (DF) is currently at 1.0.

How is ET data used to forecast my water budget?

Eastern uses daily historical ET, which is a long-term average (5 – 10 years) of annual ET. The calculation is as follows: BU = HET X CF X DF X LA X 0.62 X 0.001337

BU = Billing units allocated for your outdoor water budget (1 BU = 100 cubic feet)
HET = Sum of Historical ET values for a 30-day period in inches
CF = Conservation Factor*
DF = Drought Factor**
LA = Landscape Area in square feet
0.62 = Conversion factor to convert inches per sq. ft into gallons per sq.ft.
0.001337 = Conversion factor to convert gallons into billing units

*The Conservation Factor (CF) varies by account. Newer homes feature more water-efficient irrigation systems and are assigned their CF as follows:

• Connected prior to 9/1/2008: 0.8 CF
• Connected 9/1/2008 through 12/31/2010: 0.8 CF
• Connected 1/1/2011 through 5/31/2015: 0.7 CF
• Connected on or after 6/1/2015: 0.5 CF

**The Drought Factor (DF) is currently at 1.0.