UWM Plan - Municipal Water District of Orange County

Section 2
Water Demand
These targets are subject to revisions, as retail water suppliers have an option to update
their target in their 2015 UWMPs. Additionally, the population weightings used to
calculate these targets will be revised in 2015 and 2020 based on the most recent
compliance-year population data.
Deducting Recycled Water Used for Indirect Potable Reuse
SBx7-7 allows urban retail water suppliers to calculate a deduction for recycled water
entering their distribution system indirectly through a groundwater source. Individual
water suppliers within the OCWD Groundwater Basin have the option of choosing this
deduction to account for the recharge of recycled water into the basin by OCWD
historically through Water Factory 21, and more recently by GWRS. These deductions
also benefit all members of the Orange County 20x2020 Regional Alliance.
MWDOC has provided the documentation for the calculations of this deduction to assist
retail water suppliers if they choose to include recycled water for indirect potable reuse in
their individual targets. This calculation is applied as a deduction from the water
supplier’s calculation of Gross Water Use 3 .
Table 2-9 provides the calculation deducting recycled water for indirect potable reuse for
OCWD Basin Agencies. Because year-to-year variations can occur in the amount of
recycled water applied in a groundwater recharge operations, a previous five year average
of recharge is used, as found in column (1). To account for losses during recharge and
4
recovery, a factor of 96.5% was used in column (2) . After accounting for these losses,
the estimated volume of recycled water entering the distribution system is calculated in
column (3).
In column (4), the annual deduction for recycled water for indirect potable reuse is
expressed as a percentage of the total volume of water extracted from the basin in that
year. This is the annual percentage of total OCWD basin production that is eligible for a
deduction. For individual water suppliers in the OCWD Basin, the annual deduction is
calculated as their basin pumping in a given year multiplied by the value in column (5).
For example, if Agency A pumped 10,000 acre-feet of water from the OCWD Basin in
Fiscal Year 2004/05, then 1.47% of that total production would be deducted from the
agency’s calculation of Gross Water Use for that year as found in column (5). This
equates to a deduction of 147 acre-feet (AF).
3 The calculation is described in Step 8 of Methodology 1 from the Technical Methodologies.
4 Figure based on in-basin losses to other groundwater basins, which averages 10,000 AF per year or 3.5%
of average basin yield. The estimated FY 2090/10 basin losses of 9,315 acre-feet can be found in the Fiscal
Year 2009/10 Conjunctive Use Program (CUP) Account Activity and Losses. Losses associated with
treatment and recharge operations are negligible.
Municipal Water District of Orange County
2010 Regional Urban Water Management Plan
Final
2-12