City of Napa
2026-27
Water Supply and Demand Assessment
Assessment Period July 2026 through June 2027
For Submission to California Department of Water Resources (DWR) by July 1, 2026 ATTACHMENT 1
The City of Napa Water Supply and Demand Assessment for the period July 2026 through June 2027 is defined in the following tables as required by the California Department of Water Resources (DWR). This fifth annual assessment of anticipated demands and available water supplies must be submitted to DWR by July 1, 2026.
Water Demands. The information in Table 2 represents baseline water demands inclusive of the City’s permanent water waste prohibitions and conservation programs listed in Table 5.
Demands reflect an approximate 3% increase above 2025-26 actuals. Residential, commercial, and agricultural demands are expected to grow slightly, while commercial landscape irrigation is expected to remain flat, as post-drought trends have become settled and new state regulations may inhibit additional irrigation use. The demands listed are unconstrained by additional actions that would be taken during an officially declared water shortage (Level 1-6).
Water Supplies. The water supply information in Table 3 reflects stable post-drought scenarios for both local and imported sources. State Water Project supplies are bolstered by significant unused carryover water from previous years, and with a final 2026 North of Delta allocation of 60%, additional carryover supply will become available in 2027. State Water is limited during March due to North Bay Aqueduct annual maintenance. Winter storms filled the two local reservoirs for the fourth straight year. Lake Hennessey remains above 95% capacity as of early June 2026. Milliken Reservoir will remain unused for the entire period, as the City replaces and hardens the raw water pipeline damaged in the 2017 Atlas Fire.
As shown in Table 4, the City of Napa projects no water shortages in 2026-27.
The City of Napa declared an end to its most recent water shortage emergency back in April 2023. Subsequently the City adopted permanent water waste prohibitions that remain in effect even when no water shortage is officially declared. Table 5 is a list of actions that the City continues to implement year-round, including water conservation incentives for customers.
While the current outlook is a welcome respite from the major 2020-2023 and 2013-2016 droughts, the City understands the volatility of California’s climate and is committed to “Making Water Conservation a Way of Life” by meeting its water use targets under SB 606/AB 1668.
Demand on the City water system is projected to remain well below 132 gallons per capita per day as required by its Urban Water Use Objective.
ATTACHMENT 1
Table 1. Annual Assessment Information
Supplier is a Wholesaler
Supplier is a Retailer
If you are both a wholesaler and retailer, will you be submitting two separate reports or a combined report? Number of Reports Year Covered By This Shortage Report (Required)
Start: July 1, 2026
End: June 30, 2027
Volume Unit for Reported Supply and Demand:
(Must use the same unit throughout) AF
Supplier's Annual Assessment Planning Cycle (Required)
Start Month: July
End Month: June
Data Interval: Monthly (12 data points per year)
Water Supplier's Contact Information (Required)
Water Supplier's Name: City of Napa
Contact Name: Patrick Costello
Contact Title: Water Resources Analyst
Street Address: 1700 Second Street, Suite 100
ZIP Code: 94559
Phone Number: (707)257-9309
Email Address: [email protected]
Report Preparer's Contact Information
(if different from above)
Preparer's Organization Name:
Preparer's Contact Name:
Phone Number: (XXX)XXX-XXXX
Email Address:
Supplier's Water Shortage Contingency Plan
WSCP Title City of Napa Water Shortage Contingency Plan WSCP Adoption Date 6/16/2026
Other Annual Assessment Related Activities
Activity Timeline/ Outcomes / Links / Notes
Annual Assessment/ Shortage Report Title: 2026-27 Water Supply and Demand Assessment Annual Assessment / Shortage Report Approval Date: 6/2/2026 Other Annual Assessment Related Activities: Optional
(Add rows as needed)
Type of Supplier (Required to check one or two)
ATTACHMENT 1
Use Type Start Year: 2026 Volumetric Unit Used2: AF
Jul Aug Sep Oct Nov Dec Jan Feb Mar Apr May Jun Total by Water Demand Type
All Demands 1480 1530 1300 1010 730 710 710 660 940 910 1290 1350 12620 0 0
0 0
0 0
0 0
0 1480 1530 1300 1010 730 710 710 660 940 910 1290 1350 12620 0 0
0 0
0 0 0 0 0 0 0 0 0 0 0 0 0 0
Jul Aug Sep Oct Nov Dec Jan Feb Mar Apr May Jun Total
0 0
0 0
Three years ago total demand
Four years ago total demand
Optional (for comparison purposes)
Last year's total demand
Two years ago total demand
Table 2: Water Demands1
Projected Water Demands - Volume3
Total by Month (Non-Potable)
1Projections are based on best available data at time of submitting the report and actual demand volumes could be different due to many factors. 2Units of measure (AF, CCF, MG) must remain consistent. 3When opting to provide other than monthly volumes (bi-monthly, quarterly, or annual), please see directions on entering data for Projected Water Demand in the Table Instructions.
Notes: 2026-27 assumes total annual demand experiences linear increase toward the 2030 total in 2025 UWMP projections. Slight residential, CII, and Ag demand growth, with CII Landscape flat or declining due to AB 1572, etc. Monthly demands are projected about 3% higher than 2025-26 actuals and include contracted volumes to be delivered to St. Helena. These baseline demands are inclusive of the City's permanent water waste prohibitions and conservation programs listed in Table 5. They are unconstrained by additional actions that would be taken during a declared shortage (Level 1-6).
Total by Month (Potable)
Additional
Description
(as needed)
Level of
Treatment
for Non-
Potable
Supplies
Drop-down
list
Drop-down list
May select each use multiple times
These are the only Use Types that will
be recognized by the WUEdata online
submittal tool
(Add additional rows as needed)
Demands Served by Potable Supplies
Demands Served by Non-Potable Supplies
ATTACHMENT 1
Water Supply Start Year: 2026 Volumetric Unit Used2: AF Jul Aug Sep Oct Nov Dec Jan Feb Mar Apr May Jun
Total by
Water
Supply Type
Supply from Storage Lake Hennessey 1100 1100 1100 1100 300 300 200 100 1000 800 800 800 8700 30500 Supply from Storage Milliken Reservoir 0 0 0 0 0 0 0 0 0 0 0 0 0 2350 Purchased/Imported Water State Water Project 1050 1150 1050 1400 1250 1250 1050 1050 500 1050 1050 1150 13000 21900 0 0
0 0
0 0
0 2150 2250 2150 2500 1550 1550 1250 1150 1500 1850 1850 1950 21700 0 0 0
0 0
0 0 0 0 0 0 0 0 0 0 0 0 0 0 0
Jul Aug Sep Oct Nov Dec Jan Feb Mar Apr May Jun Total
0 Potable Supplies
Non-Potable Supplies
eAR Reported Total Water Supplies
Optional (for comparison purposes)
1Projections are based on best available data at time of submitting the report and actual supply volumes could be different due to many factors. 2Units of measure (AF, CCF, MG) must remain consistent. 3When opting to provide other than monthly volumes (bi-monthly, quarterly, or annual), please see directions on entering data for Projected Water Supplies in the Table Instructions.
Notes: Lake Hennessey supplies reflect a reservoir at >95% capacity as of early June 2026. State Water Project supplies reflect significant carryover supplies from previous years and a 2026 60% Table A North of Delta allocation. The Milliken Treatment Plant will remain offline, awaiting completion of repairs for the raw water pipeline damaged in the 2017 Atlas Fire.
Column Q represents the annual diversion and storage Water Rights for the two local reservoirs and the City's contractual 100% Table A allocation for the State Water Project.
Total by Month (Potable)
Total by Month (Non-Potable)
Table 3: Water Supplies1
Projected Water Supplies - Volume3
Water
Quality
Drop-down
List
Total Right
or Safe
Yield*
(optional)
Additional Detail on
Water Supply
Drop-down List
May use each category multiple
times.These are the only water
supply categories that will be
recognized by the WUEdata online
submittal tool
(Add additional rows as needed)
ATTACHMENT 1
Table 4(P): Potable Water Shortage Assessment1
Start Year: 2026 Volumetric Unit Used2: AF
Jul Aug Sep Oct Nov Dec Jan Feb Mar Apr May Jun3 Total
Anticipated Unconstrained Demand 1480.0 1530.0 1300.0 1010.0 730.0 710.0 710.0 660.0 940.0 910.0 1290.0 1350.0 12620.00 Anticipated Total Water Supply 2150.0 2250.0 2150.0 2500.0 1550.0 1550.0 1250.0 1150.0 1500.0 1850.0 1850.0 1950.0 21700.00 Surplus/Shortage w/o WSCP Action 670.0 720.0 850.0 1,490.0 820.0 840.0 540.0 490.0 560.0 940.0 560.0 600.0 9,080.0 % Surplus/Shortage w/o WSCP Action 45% 47% 65% 148% 112% 118% 76% 74% 60% 103% 43% 44% 72% State Standard Shortage Level 0 0 0 0 0 0 0 0 0 0 0 0 0 Benefit from WSCP: Supply Augmentation 0.0
Benefit from WSCP: Demand Reduction 0.0
Revised Surplus/Shortage with WSCP 670.0 720.0 850.0 1490.0 820.0 840.0 540.0 490.0 560.0 940.0 560.0 600.0 9080.0 % Revised Surplus/Shortage with WSCP 45% 47% 65% 148% 112% 118% 76% 74% 60% 103% 43% 44% 72% = Auto calculated
= For manual input
Table 4(NP): Non-Potable Water Shortage Assessment 1
Start Year: 2026 Volumetric Unit Used2: AF
Jul Aug Sep Oct Nov Dec Jan Feb Mar Apr May Jun3 Total
Anticipated Unconstrained Demand: Non-Potable 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.00 Anticipated Total Water Supply: Non-Potable 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 Surplus/Shortage w/o WSCP Action: Non-Potable 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 % Surplus/Shortage w/o WSCP Action: Non-Potable
Benefit from WSCP: Supply Augmentation 0.0
Benefit from WSCP: Demand Reduction 0.0
Revised Surplus/Shortage with WSCP 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 % Revised Surplus/Shortage with WSCP
1Assessments are based on best available data at time of submitting the report and actual volumes could be different due to many factors. 2Units of measure (AF, CCF, MG) must remain consistent. 3When optional monthly volumes aren't provided, verify Tables 2 and 3 use the same columns for data entry and are reflected properly in Table 4 and make sure to use those same columns to enter the benefits from Planned WSCP Actions. Please see directions on the shortage balancing exercise in the Table Instructions. If a shortage is projected, the supplier is highly recommended to perform a monthly analysis to more accurately identify the time of shortage. 4If you enter any WSCP Benefits, then you must enter the corresponding planned Actions into Table 5.
Planned WSCP Actions4
1Assessments are based on best available data at time of submitting the report and actual volumes could be different due to many factors. 2Units of measure (AF, CCF, MG) must remain consistent. 3When optional monthly volumes aren't provided, verify Tables 2 and 3 use the same columns for data entry and are reflected properly in Table 4 and make sure to use those same columns to enter the benefits from Planned WSCP Actions. Please see directions on the shortage balancing exercise in the Table Instructions. If a shortage is projected, the supplier is highly recommended to perform a monthly analysis to more accurately identify the time of shortage. 4If you enter any WSCP Benefits, then you must enter the corresponding planned Actions into Table 5. = From prior tables
Planned WSCP Actions4
ATTACHMENT 1
July 1, 2026 to June 30, 2027
Enter Amount
(Drop-down
List)
Select % or
Volume Unit
Start Month End Month
0 (No Shortage) Offer Water Use Surveys Yes July June
0 (No Shortage) Provide Rebates on Plumbing Fixtures and Devices Yes July June
0 (No Shortage) Provide Rebates for Landscape Irrigation Efficiency Yes July June
0 (No Shortage) Provide Rebates for Turf Replacement Yes July June 0 (No Shortage) Other - Require automatic shut of hoses Yes Jul y June 0 (No Shortage) Other - Prohibit use of potable water for washing hard surfaces Yes July June
0 (No Shortage) Landscape - Restrict or prohibit runoff from landscape irrigation Yes July June
0 (No Shortage) Landscape - Other landscape restriction or prohibition Yes July June
0 (No Shortage)
Other - Customers must repair leaks,
breaks, and malfunctions in a timely
manner
Yes July June
0 (No Shortage) Landscape - Limit landscape irrigation to specific times Yes July June
NOTES:
Notes Section to be used only
fo
r clarifying details, and not
for listing specific actions.
Actions must be entred into
table rows above.
1If you plan Supply Augmentation Actions then you must enter WSCP Benefits from Supply Augmentation Actions into Table 4. If you plan Demand Reduction Actions then you must enter WSCP Benefits from Demand Reduction Actions into Table 4. 2If an Action is planned to be implemented in multiple non-contiguous periods of the year, please make separate entries on multiple rows for the same action spanning the different implementation periods.
Table 5: Planned Water Shortage Response Actions
Add additional rows as needed
How much is action going to
reduce the shortage gap?
(O
ptional)
When is shortage response
action anticipated to be
imp
lemented2?Is action
already being
imp
lemented?
(Y/N)
ACTIONS1: Demand Reduction, Supply
Augmentation, and Other Actions.
(Drop-down List)
These are the only categories that will be
accepted by the WUEdata online submittal
tool. Select those that apply.
Anticipated Shortage
Level
Dro
p-down List of
State Standard Levels (1 -
6) and Level 0 (No
Shortage)
Demand Reduction Actions listed above are permanent water waste prohibtions and water conservation program offerings for City of Napa customers. They remain in effect at all times, even when no water shortage is declared.
ATTACHMENT 1