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Water Supply Roadmap

Image shows a lake surrounded by verdant hills, and the following text superimposed in blue with a white background: "Roadmap to Water Supply Reliability."

Marin Water’s Water Supply Roadmap is a long-term, adaptive strategy designed to ensure a reliable, resilient water supply for the communities we serve. The roadmap was developed following the 2020–2022 drought emergency and identifies a portfolio of projects to address projected supply gaps and changing climate conditions. The roadmap integrates both demand reduction (through water efficiency) and new supply projects to meet Marin Water’s goal of ensuring 8,500 acre-feet per year (AFY) of resilient water supply.

The District is actively advancing its most promising and cost-effective projects while remaining flexible to new information and opportunities.
 

What’s New (August 2025)
  • Nicasio Spillway Project no longer active: After further analysis, work to develop this project has stopped.
  • New ARC Project Page: The Atmospheric River Capture Project now has a dedicated webpage: marinwater.org/ARCproject
  • Updated Roadmap Focus: Current priorities include water efficiency; the Atmospheric River Capture project; and in-system improvements including Soulajule system upgrades.

Water Supply Goal

Resiliency Goal: 8,500 AFY
This goal was set following the Strategic Water Supply Assessment and remains the benchmark guiding current and future water supply planning efforts.
 

Priority Elements of the Roadmap

The Roadmap is organized into five broad strategies, each with a range of projects, that – when integrated – are designed to address the District’s water supply needs to ensure a more resilient system. Double-click on each button below to expand details on the range of proposed and/or underway projects currently within each strategy.

Conservation – Water Efficiency Master Plan Implementation, AMI, Water Loss Control

Water conservation continues to be a cornerstone of the roadmap. Based on updated supply demand projections and historical customer performance, Marin Water projects that, long-term, water efficiency will reduce the District's overall 8,500 AFY water supply goal by 2,000 AFY.

Water Efficiency Master Plan Implementation

Marin Water is continuing its strong conservation efforts and will work to gain additional savings through implementation of the strategies in the District’s comprehensive and innovative Water Efficiency Master Plan. 

People sit around a table with a blue tablecloth. Posters with information appear on the wall behind.
Intensive study and robust customer feedback will yield beneficial changes to water rules, ordinances and incentive structures via the District’s Water Efficiency Master Plan.

 

Advanced Metering Infrastructure (AMI)

Advanced Metering infrastructure (AMI) is technology which allows customers to receive real-time data from their water meters, helping them to detect leaks or abnormal water usage and gain greater understanding of their household or business water use patterns. Marin Water is currently testing various types of this technology as it plans for a service area-wide rollout of AMI by 2030.

Advanced Metering Infrastructure graphic which shows a grey illustrated cellular tower transmitting water use data between a blue illustrated home with an AMI water meter and a blue illustrated Marin Water building.

 

 

 

 

 

Water Loss Control 

Marin Water has long operated a proactive Leak Reduction Program to identify and address in-system water loss. A recent program review identified new opportunities to strengthen this work, several of which are now being implemented or tested as part of the Water Supply Roadmap.

Acoustic Leak Detection Pilot
The District’s core approach uses leak noise amplifiers to manually survey about 200 miles of pipeline each year, detecting leaks that might otherwise go unnoticed. While this traditional method is effective, Marin Water is now piloting newer acoustic leak detection technologies in two neighborhoods – Santa Venetia and Spinnaker Point. The pilot is testing three types of systems:

  • Hydrant-based sensors, which detect leaks in water mains between hydrants.
  • Meter-integrated sensors, installed near customer meters to monitor nearby pipelines.
  • Valve-based sensors, that are attached to valves in the distribution system and can detect leaks in the pipelines.

The different systems are based on similar technologies and are being deployed in both neighborhoods to assess their performance, responsiveness, and potential for broader use.

In-System Improvements - Soulajule Enhancements, Phoenix-Bon Tempe Connection, Forecasting and Stream Release Automation

Electrify Soulajule Pump Station

Estimated Water Supply = 420 acre-feet per year

Soulajule Reservoir, located in western Marin, holds approximately 10,572 acre-feet of water – 13% of the District’s total local reservoir capacity. However, without a direct electrical connection, water can only be pumped from Soulajule to Nicasio Reservoir using portable diesel generators, limiting its use. This project would extend electrical power to the Soulajule Pump Station, enabling more routine and efficient transfers of water into the broader system. Electrification would support both operational flexibility and future efforts to store imported winter water, enhancing Marin Water’s ability to manage supplies more effectively.

Aerial photo shows a body of water held back by an earthen dam, with spillway along the right side.
Electrifying the Soulajule Pump Station will decrease reliance on generators and improve efficiency for long-term operating models.

 

Phoenix-Bon Tempe Connection  

Estimated Water Supply = 260 acre-feet per year 

Although Phoenix Lake is one of Marin Water’s smallest reservoirs (411 acre-feet), it receives an average of 3,665 acre-feet in annual inflow. Currently, logistical challenges limit the District’s ability to move this water uphill to Bon Tempe Reservoir and its treatment plant. This project would establish a permanent pipeline between Phoenix Lake and Bon Tempe, enabling more frequent use of Phoenix’s inflows. In addition to improving water supply reliability, the project has a secondary benefit of reducing flood danger to the communities of Ross and San Anselmo by increasing storm water storage capacity in the Phoenix basin. 

Given the relatively small water supply benefit, this project is not being prioritized at this time.

Map shows the location of a planned pipeline connecting two reservoirs.
Connecting the Phoenix and Bon Tempe reservoirs will increase operational efficiency by allowing more frequent use of Phoenix Lake water.

 

Forecasting and Stream Release Automation   

To improve streamflow management and forecasting accuracy, Marin Water is enhancing its monitoring infrastructure. Streamflow measurement equipment has been installed near Shafter Bridge, with additional installations planned at Walker Creek in late 2025. These tools will help the District better manage environmental releases and optimize reservoir operations, particularly during storm and drought periods.

People gather around a stream gauge at the edge of a creek.
New stream gauges can add important data points to help automate stream releases from District reservoirs, reducing water waste in the process.

 

Conveyance – Atmospheric River Capture Project

A new 13-mile pipeline would connect the North Marin Aqueduct to Nicasio Reservoir, allowing winter water from the Russian River to be stored for later use. The process for preliminary design and environmental review for this project is now getting underway.

Spillway Modifications for Storage Enlargement - Nicasio and other spillways

Nicasio Spillway Modification

Estimated Increase in Water Storage Capacity = approximately 3,700 acre-feet per year 

Nicasio Reservoir was created by the construction of Seeger Dam, an earthen filled dam on Nicasio Creek in 1960. The reservoir's current storage capacity is 22,340 acre-feet. This project proposes installing a 280-foot-long, 4.4-foot-high inflatable rubber gate spanning the width of the existing spillway crest of Seeger Dam to increase the capacity at Nicasio Reservoir by approximately 3,700 acre-feet. The additional water supply yielded through this project could help increase the District's water supply resiliency during future droughts. 

After extensive evaluation, Marin Water is no longer actively pursuing the proposed Nicasio Spillway Modification Project. While initial investigations suggested the potential for added reservoir storage at a relatively low cost, further study revealed:

  - Significantly higher costs than originally anticipated
  - Potential reductions in environmental yield
  - Complex regulatory, ecological, and social considerations

The District will retain all work completed to date for future reference, but the project has been withdrawn from CEQA review and removed from active planning. 

Other Spillway Modifications

The District continues to evaluate its other reservoir spillways to determine if there are potential opportunities to gain additional storage capacity through modifications to any of them.

Other Projects - Kent Lake Storage Enlargement, Desalination, Recycled Water

Kent Lake Storage Enlargement

Estimated water yield: 5,000 acre-feet per year

Marin Water has examined storage expansion projects at Kent Lake and at Soulajule Reservoir. Both projects would yield an additional 5,000 acre-feet per year, but based on environmental and private property factors, the District is focusing its ongoing work on storage expansion at Kent Lake, the District’s largest reservoir. 

Located within a highly productive watershed, Kent Lake fills consistently with rainfall most years. Building on this proven reliability, the Kent Lake expansion project proposes to raise the existing dam at Kent Lake to increase the capacity of the reservoir by 20,000 acre-feet, making the new total capacity about 53,000 acre-feet. Rainfall would fill this additional available storage, which would serve as an emergency drought reserve. 

The District will continue to investigate the feasibility of expanding this reservoir. 


Desalination 

Estimated Water Supply = 10,000 acre-feet per year

A treatment plant would be constructed along the Bayshore in San Rafael to purify bay water for use within the District’s system, delivering up to 10,000 acre-feet of water in a drought year, or about 25% of potable demand including environmental releases. The project would require significant storage and pumping to assist with integrating the treated water into Marin Water’s system to allow the plant to deliver up to its maximum rate of 10 million gallons per day. The desalination process would produce brine as a byproduct of the treatment process; that brine would be added to the existing Central Marin Sewer Agency outfall, thereby reducing the need to build a dedicated outfall. 

The District will continue to monitor desalination technological advances and cost. 


Recycled Water 

Estimated Water Supply = 81-285 acre-feet per year

A variety of potential routes for expanding recycled water use in Marin County have been reviewed, including a project involving the Sewage Agency of Southern Marin, which would yield 81 acre-feet per year, to expanded recycled water pipeline along Peacock Gap to generate an additional 285 acre-feet per year. 

The District continues to pursue outside funding opportunities for smaller recycled water projects that make sense for our service area. 

 

Adaptive Roadmap Strategy

The roadmap is not a static plan, but an adaptive framework that allows Marin Water to pursue the most effective projects while remaining flexible as new information, technologies, or climate scenarios emerge. Future potential additions – such as expanded ARC phases, regional partnerships, or new storage technologies – will continue to be evaluated.
 

Progress Toward the Goal 

Roadmap Projections as of August 2025 Update:

ComponentEstimated Yield (Acre Feet per year)
Water efficiency2,000
ARC (Phase 1)3,800 - 4,750
In-System Improvements         1,000 - 1,500
Soulajule Enhancements~420
Total Identified Supply7,220 - 8,670

How We Got Here

Aerial view of Nicasio Reservoir in drought conditions

After recovering from a water shortage emergency in 2021, Marin Water set to work to strengthen the resiliency of its water supply to prepare for future droughts. A strategic water supply assessment was launched, and it guided development of the integrated Water Supply Roadmap being pursued today. Below is a timeline of events, actions and changes in the direction of the Roadmap over the last several years.

2020
  • Onset of drought
  • Sustained and innovative water efficiency begins from onset of drought through today
2021
2022
2023
2024
2025


Stay Informed

Sign up for Marin Water’s monthly eNews  
Subscribe at marinwater.org/enews. 

Review Board Presentations on Roadmap Efforts
Since the launch of Marin Water’s water supply resiliency planning process, updates and key decisions have been shared during Board and Committee meetings, which are open to the public. Below, you can find a compiled record of those meetings, including links to related agendas, presentations, and video recordings.

Strategic Water Supply Assessment | Water Supply Roadmap | Conveyance & Storage | Desalination & Recycled Water | Nicasio Spillway Modification | Soulajule Pump Station Electrification | Phoenix Lake to Bon Tempe Reservoir Connection | Water Efficiency Master Plan

Strategic Water Supply Assessment 
Water Supply Roadmap 
Conveyance & Storage 
Desalination & Recycled Water 
Nicasio Spillway Modifications 
Soulajule Pump Station Electrification 
  • December 19, 2023 – Board of Directors Regular Meeting 
    Agenda Item 8e: Professional Services Agreement with Kennedy/Jenks Consultants, Inc. for Engineering Services for the Soulajule Pipeline Project 
    Watch meeting recording and view documents
  • July 21, 2023 – Operations Committee Meeting/Special Meeting of the Board of Directors 
    Agenda Item 5: Water Resilience Roadmap – Update on Phoenix and Soulajule Projects 
    Watch meeting recording and view documents 
Phoenix to Bon Tempe Reservoir Connection 
  • June 18, 2024 – Board of Directors Regular Meeting 
    Agenda Item 9a: Adoption of the Final Initial Study/Mitigated Negative Declaration for Phoenix-Bon Tempe Connection Project and Approval of the Phoenix-Bon Tempe Connection Project 
    Watch meeting recording and view documents
  • March 8, 2024 – Operations Committee Meeting/Special Meeting of the Board of Directors 
    Agenda Item 4d: Phoenix-Bon Tempe Connection Project Update 
    Watch meeting recording and view documents
  • December 19, 2023 – Board of Directors Regular Meeting 
    Agenda Item 8d: Professional Services Agreement with Hazen and Sawyer for Engineering Services for design of the Phoenix-Bon Tempe Pump Station Design Project 
    Watch meeting recording and view documents
  • July 21, 2023 – Operations Committee Meeting/Special Meeting of the Board of Directors 
    Agenda Item 5: Water Resilience Roadmap – Update on Phoenix and Soulajule Projects 
    Watch meeting recording and view documents
  • February 18, 2022 – Operations Committee Meeting/Special Meeting of the Board of Directors 
    Agenda Item 3 – Phoenix Lake Raw Water Transfer Pump Station Presentation 
    Watch meeting recording and view documents 
Water Efficiency Master Plan