Setting a Water Budget

There are several different approaches, methods, and technologies that can be used to establish water budgets, which are the specific amount of water allotted to each customer. Each agency uses slightly different equations to calculate these water budgets and commonly allocations are separated into indoor water use and outdoor use. Equations may also differ depending on the source of water; for instance, recycled water versus potable water. Beyond that, the different customer classes (e.g., residential, dedicated irrigation, commercial, industrial, and institutional or public) often utilize different calculations.

Each water budget equation needs specific data on each customer in order to develop a water allocation unique to that customer’s water needs. This data may be measured for each customer or estimated using a variety of sources and analysis techniques, depending on the data in question. The indoor water budget generally relies on information on the number of people per household and the amount of water each person uses each day. The outdoor water budget focuses on determining the landscaped or irrigated area, the evapotranspiration rate, and the monthly conservation factor (or crop coefficient) often based on state guidelines for outdoor landscaping. However, these data needs may change based on the customer type and source of water.


Changes to data once a water budget is established is discussed further in Variances and Long-Term Maintenance »

In many cases, customers are contacted first to confirm data even before BBRs are implemented. Case studies where this occurred may be found below as well as in Customer Outreach, Support, and Service » .

The following pages, by agency, describe the basis for establishing water budgets under a number of different conditions, the technologies used to acquire and process necessary data, and different methods to apply water budgets based on an agency’s specific needs.

Easter Municipal
Water District
As the State releases stricter landscape water use guidelines through MWELO, EMWD adopts a new, lower conservation factor for new water accounts. Each new factor reduces the outdoor water budget, thereby promoting more efficient landscaping and watering. As of June 2015, EMWD has 4 conservation factors. img
Elsinore Valley
Municipal Water District
EVMWD discusses its structure and some of its implementation assumptions. For instance, a seasonality factor helps outdoor budgets remain consistent from month to month. The persons per household baseline was set higher than the Census to ensure fairness. Irrigated area is initially assumed to be 60% of the parcel area. img
Irvine Ranch Water District IRWD discusses how it sets up water budgets, including landscape area, indoor allocation, and modifications since adoption for updated plumbing codes and increased conservation efforts. Recycled water and CII customers’ budgets are likewise described. img
Las Virgenes Municipal
Water District
Equations for residential, irrigation, commercial, and recycled water customers are described. LVMWD determines irrigated area using four-band aerial imagery. Lessons learned and issues that came up (e.g., time of year to capture imagery, right- of-way lines, and multi-family complexes) are described. img
Rancho California
Water District
RCWD uses rolling budgets, which allow
customers to make up for wasteful water use with extra efficient use within the same fiscal year. The two-step billing process was suspended during the drought.
Valencia Water Company CPUC approved VWC’s residential and dedicated irrigation water budgets. Outdoor water budgets for both are split up to limit certain types of landscaped areas. For residential customers, the crop coefficient requires more efficiency past the first 2,500 square feet of landscaped area and customers are limited to 10,000 square feet. For dedicated irrigation customers, areas of active play and areas with edible plants have a lower crop coefficient. img
Western Municipal
Water District
The indoor and outdoor water budgets for WMWD’s customers include different default values for household size, GPCD, and annual average ET adjustment factor (e.g., budget adjustment coefficient using MWELO). CII customers have budgets based on a three year rolling average. img

Evapotranspiration (ET), as mentioned above, is a typical component of the outdoor water budget equation, but there are different ways to determine the ET value to use for an individual customer. Typically, reference ET (ETo) is determined from meteorological data or pan evaporation and is based on a standardized vegetation. Crop-specific ET can then be calculated based on the unique crops observed in the region. Agencies have a variety of different ways to determine the evapotranspiration, as discussed in Evapotranspiration Data Sources »

Water agencies have been severely impacted by the ongoing drought that began in 2012. Some agencies have restricted water use and encouraged greater conservation via water budgets, as discussed in Relation to Drought Response/Water Shortage » These techniques, though specific to the current drought, also apply during any water shortage situation.