How are residential water budgets calculated?
Western's customers are provided with a total monthly water budget. The total monthly water budget includes a customer's indoor water budget (Tier 1) and outdoor water budget (Tier 2). The number of billing units in your total monthly water budget varies each month depending on days within the billing cycle and local weather information. Therefore, customers may receive a higher water budget during longer billing cycles and also in the warmer summer months.
Indoor Water Budget
The indoor budget is calculated using four factors:
- The number of people in the household
- The average amount of water an efficient person uses daily
- The number of days in the billing cycle
- A conversion factor from gallons to billing units
For example, for a 3-person household during a 30-day billing cycle the indoor water budget would be:
Indoor water budget = 3 X 60 X 30 = 5,400 gallons of water / 748 gallons = 7.2 billing units
People per household
Based on census data, Western uses a default number of three people per household for single-family homes and two people per household for condominiums and apartments. The number of people regularly living in your home directly impacts your indoor water budget. If you need to update the number of people in your home, complete the Standard Request for Water Budget Adjustment Form (Spanish).
Average daily water use
Studies show that, on average, a typical person uses less than 60 gallons of water each day indoors. This amount includes all indoor water use such as hydration, bathing, doing laundry, and more while using common water-efficient devices, including low-flow toilets and showerheads. Based on this data, and a review of our customers’ historical water use, Western uses an indoor water budget of 60 gallons per person per day.
Days in the billing cycle
The number of days that you are being billed for service. This information can be located on your bill and comes from the actual dates your meter is read. It may differ from bill to bill, but will usually be between 28 and 31 days.
Outdoor Water Budget
The outdoor budget is calculated using three factors:
- Irrigated landscape area
- Daily localized weather data
- Landscape factor
For example, for a property with 5,000 square feet of irrigated landscape area and an ET for May of 5.72 inches the outdoor water budget would be:
Outdoor water budget = 5,000 x 5.72 x 0.8 x .62 = 14,186 gallons of water / 748 gallons =19 billing units
Irrigated landscape area
The irrigated landscape area is the amount of landscaped area on your property that receives regular watering. Pools and spas are also included in the irrigated acreage because they use approximately the same amount of water (due to evaporation and refilling) as a lawn does. Western may use Riverside County Assessor parcel data or its geographic information system (GIS) to determine the default irrigated area for your home.
Localized weather data (Evapotranspiration or ET)
The amount of water that is lost each day from your landscaping due to evaporation and plant transpiration is known as evapotranspiration (ET), and it varies daily due to factors such as wind, humidity and temperature. Western measures ET daily using a system that calculates precise weather data for more than 460 distinct microclimate zones within our retail service area. ET values change with the weather, so the water budget for landscapes is larger in hot weather and smaller in cooler weather.
The landscape factor measures the specific amount of irrigation water required by each type of plant in your yard. The rate structure is based on the assumption that landscaped areas are a mix of grass, trees, shrubs and ground cover, which combine for a landscape factor of 0.8. If your landscaping is mostly grass and you water it wisely, you can easily stay within your outdoor water budget. If your landscaping includes drought-tolerant plants and you water it wisely, you’ll have an even easier time staying within your outdoor water budget. Customers requesting new water service (installing a new water meter) from Western after January 1, 2012, receive a landscape factor of 0.7.