Major Elements of the Obligation and Enrollment Projections for the

Major Elements of the Obligation and Enrollment
Projections for the 2015 Plan of Operation
1. Projections are generated from a computer model developed by CAP staff
2. The model simulates supply and demand conditions within CAP's 3-county service area
3. Required data have been collected from a variety of sources, including ADWR, the U.S.
Census Bureau, county assessor offices, the Arizona Corporation Commission, the
Associations of Governments, and internal sources at CAP
4. The 80 public and private water providers simulated in the model account for 99% of the
municipal sector demand
5. The model also performs calculations that are specific to the Assured Water Supply Rules and
1. Projections of new and existing demand are developed for each water provider
2. Existing demand is projected to decline by 0.5% per year, based on observed trends in water
use efficiency
3. New demand is based on projected housing units, and a gallons per housing unit per day
(GPHUD) factor that is unique to each water provider
4. Housing units are derived from detailed growth projections developed by the Associations of
Governments, (MAG, CAG & PAG), which are themselves tied to Arizona's official countylevel projections
5. Provider-specific GPHUDs for new housing units are based on total demand divided by total
housing units
6. The GPHUDs for new housing units are projected to decline by 0.1% per year
7. There are additional calculations for water providers serving CAGRD Member Lands
a. Projected housing units are differentiated between lots enrolled under previous
Plans, versus new enrollment and construction
b. Subdivision-level GPHUDs were developed for Member Lands that have enrolled, but
unbuilt lots at the beginning of the Plan period
1. The model contains a unique portfolio of physical and legal supplies for each water provider
(e.g., effluent, surface water, groundwater, CAP, and long-term storage credits)
2. The projected demand of a water provider is fulfilled by using each available supply, in a
priority preference order, until the entire demand is satisfied
3. The model was refined and calibrated by comparing results against historic use of supplies
1. For Member Service Areas, Excess Groundwater reported to the CAGRD is one of the
available supply types, but is last in preference order
2. For water providers serving Member Lands, the amount of obligation is based on the
demand of the new and existing Member Land subdivisions, taking into consideration the
availability and use of groundwater allowances, as well as the water providers' overall
groundwater reliance
1. The City of Buckeye is projected to become a Member Service Area in 2015
2. Enrollment of new Member Lands is based on the housing unit projections, and the
proportion of new units associated with the 2015 Plan