Marin Water Supply and the Atmospheric River Capture Project

Fifty thousand cubic yards. That is how much sediment and brush Marin Water now says it will dig out of Upper Nicasio Creek and Halleck Creek, roughly 5,000 ten-yard dump-truck loads by our count, as part of its Atmospheric River Capture Project. The number showed up in a revised Notice of Preparation filed September 17, 2026, and it tells you the pipeline plan is getting bigger, not smaller.

The short answer on Marin water supply: it is in far better shape than in 2021, when reservoirs fell to 32 percent, but it still leans on rain that falls in a few winter months. ARC is the district's bet on fixing that. Buyers should read it as a modest insurance policy with a real price tag.

Is Marin's water supply secure right now?

Yes, for this year. On September 16, 2026, Marin Water's seven reservoirs held 65,846 acre-feet, 82.8 percent of capacity, about 19 percent above the long-run average for that date.

The risk is two dry winters back to back, which is what happened in 2020 and 2021. About 75 percent of the district's water is local rain caught on Mount Tamalpais and the West Marin hills, and the rest comes from the Russian River.

What the revised filing adds

The new piece is creek work, and a lot of it. The March 2026 version of the plan was a pipeline and two pump stations. The September supplement adds a long-term management plan for Upper Nicasio Creek, where the creek meets the reservoir in the unincorporated village of Nicasio.

Per the filing on CEQAnet (state clearinghouse number 2026030496):

• About 50,000 cubic yards of vegetation and sediment removal over at least two construction seasons.
• Roughly 3,150 linear feet of Upper Nicasio Creek and 1,200 linear feet of Halleck Creek.
• Lowering the sediment delta in Nicasio Reservoir by about 4 feet to create a bench about 100 feet wide along 2,000 feet of creek bank.
• Follow-up maintenance estimated at 10,000 cubic yards every 5 to 10 years, per the supplemental notice itself.

The filing does not say why the creek plan was added. The maintenance line is the tell: this is recurring work, not a one-time job.

A pipeline sized for storms, measured in weeks

ARC works like this. When the Russian River runs high in winter and its minimum stream flows are met, Marin Water would take extra water through the existing North Marin Aqueduct, then push it through a new 36-inch pipe to Nicasio for storage. The filing lists capacity at 30 million gallons a day.

Our math: 30 million gallons is about 92 acre-feet a day. Hitting the district's best-case 3,800 acre-feet would take roughly six weeks of full-throttle pumping. A critique published by CalSPORT in June 2026 argues the conditions for that (low reservoirs plus big Sonoma storms) rarely line up. The draft EIR should answer that with modeled years.

It is also the second try. Marin Water dropped its plan to raise the Nicasio spillway in August 2025 over rising costs and limited benefit. The district's Water Supply Roadmap counts ARC for 3,800 to 4,750 acre-feet a year toward a goal of 8,500.

October 2021 is the number that explains the whole project. Lake Lagunitas got less than half its usual 50-plus inches the winter before, storage fell to 25,772 acre-feet on October 18, 2021, and the district was planning an emergency pipeline across the Richmond-San Rafael Bridge. Then one atmospheric river hit and storage jumped to 34,535 acre-feet in a week. Weather bailed Marin out. ARC is a bet on needing that luck a little less.

Novato drinks from a different pipe

Marin Water serves central and southern Marin, about 191,000 people from San Rafael to Sausalito. Novato is served by North Marin Water District, which relies on Russian River water from Sonoma Water for about 80 percent of its supply and Stafford Lake for the rest.

Here is the local twist. ARC's pipeline would run under Novato streets, Wood Hollow Drive, Redwood Boulevard, San Marin Drive and Novato Boulevard, with a pump station near Stafford Lake. Novato gets the construction. The stored water goes to the other district.

The table puts water supplier next to Houseberry's August 2026 prices and scores.

Novato is the cheapest city in our Marin set at $1.19 million, and its water depends least on local rain. Santa Rosa sits on the same Russian River ARC wants to tap, while EBMUD's supply starts in the Sierra. None of that shows up in a listing.

Rates are the part buyers actually pay

Rates are already up, and ARC has not been built yet. Under the schedule Marin Water adopted in 2023, a typical single-family bill went from $138.66 to $218.80 every two months, the last step landing July 1, 2026.

That schedule is now used up. Marin Water plans to pay for ARC with bonds, and bonds get repaid from rates. Expect the next rate cycle to carry some of the $195 million.

What this does and does not mean

It does mean central and southern Marin is shoring up supply, and water costs there are rising faster than inflation. It does not mean Marin is running out of water. At 83 percent full, it is not.

And it does not change what drives a home's value in Mill Valley or San Rafael. A water bill that is up about $480 a year since 2023 is noise next to a $1.84 million median price. Where it matters is a repeat of 2021: mandatory cutbacks and brown lawns.

I am for ARC in principle. A district that almost ran dry five years ago should store more water. But I want the draft EIR to show how often the pipe would really run.

Questions buyers ask about Marin water

Does Marin have water restrictions right now?

No. Marin Water lifted most drought restrictions in early 2022 after October and December storms refilled reservoirs to about 95 percent. Storage is above average in September 2026.

Which Marin towns does ARC help?

Towns served by Marin Water: San Rafael, Mill Valley, Corte Madera, Larkspur, San Anselmo, Fairfax, Ross, Sausalito, Tiburon and Belvedere, plus unincorporated areas such as Kentfield. Novato is on North Marin Water District.

How do I comment on the Atmospheric River Capture Project?

Email arcproject@marinwater.org, or mail Marin Municipal Water District, c/o Lucy Croy, 220 Nellen Avenue, Corte Madera, CA 94925, by noon on October 19, 2026. The district's ARC page says the draft EIR is expected this fall.

Should water supply change where I buy in Marin?

Rarely by itself. Treat it like fire insurance: a line item to check, not a deal breaker.

That is the neighborhood-first habit we built Houseberry around, checking what sits under the address before falling for it. Our Marin neighborhood rankings and the earlier look at Marin's most affordable neighborhoods are good places to start that comparison.

Sources

CEQAnet, Supplemental Notice of Preparation, Atmospheric River Capture Project, SCH 2026030496, Marin Municipal Water District, received September 17, 2026

Marin Water, Atmospheric River Capture (ARC) Project page, retrieved September 22, 2026

Marin Water, Water Watch reservoir storage, as of September 16, 2026

Marin Water, Water Supply Roadmap, retrieved September 22, 2026

Marin Water, 2023 Water Rate Setting

Marin Water, Notice of Exemption for Temporary Urgency Change petition, August 30, 2021

National Drought Mitigation Center, Drought Impact Reporter, Marin County storage and pipeline reports, 2021 to 2022

CBS News Bay Area, “Drought-Stricken Marin Putting Into Place Tough Water Use Restrictions,” April 2021

Point Reyes Light, “Marin Water drops Nicasio spillway plan,” August 27, 2025

CalSPORT, “Marin Water’s Atmospheric River Capture (ARC) Project Unlikely to Live up to its Name,” June 5, 2026

North Marin Water District, rate increase and rate structure changes page

East Bay Municipal Utility District, water supply page

Houseberry, city guides for San Rafael, Novato, Mill Valley, Corte Madera, Larkspur, San Anselmo, Oakland and Santa Rosa, and Marin neighborhood rankings, retrieved September 22, 2026