Walk a country property in Glen Ellen or up toward Kenwood this month and the well will come up in conversation before the kitchen does. Everyone asks about the well. Fewer people ask the follow-up question that actually matters: who checks that the water coming out of it is safe to drink.

The answer surprises most buyers. Sonoma County will tell you, in exacting technical detail, how deep your casing must run, how the annular seal must be poured, and how many gallons per minute your well has to sustain before a building permit gets issued. What the county will not do, and what no state agency will do either, is test whether that water is safe. Private well water in California is not regulated by any government agency. The responsibility for testing it sits entirely with the property owner, seller and buyer alike, working it out between themselves during escrow.

That gap between engineering oversight and water-quality silence is the thing worth understanding before you write an offer on acreage in Sonoma Valley, and it is the thing worth getting ahead of before you list one.

The clock that is already running

Here is the part with a real deadline attached to it. Sonoma County requires dry weather well testing for building permits on new or replacement dwellings in marginal or scarce water zones, and that testing has a season. It typically runs from July 15 to October 1 each year. Shallow wells, defined as 50 feet deep or less, cannot get an extension past October 1 no matter what. Deeper wells can sometimes run longer, but only until countywide rainfall crosses a threshold the county tracks against Press Democrat rain gauge data.

Today is August 17. If you are planning to list a well-served country home this fall and haven't already scheduled a sustained-yield test, you are inside a closing window, not a comfortable planning horizon. The test has to demonstrate one gallon per minute per dwelling from the well, spring, or combination of sources, and it has to be performed by a licensed water well contractor, pumping contractor, or a registered engineer or geologist who notifies the county 24 hours ahead of time.

Miss the window and you are not failing an inspection so much as waiting for next summer to prove your water supply, which is its own kind of price conversation with a buyer.

The rule the county enforces, and the one it deliberately doesn't

Permit Sonoma's own guidance is direct on this point: private well water is not regulated by any government agency, and it is the property owner's job to have it tested by a state-certified lab. That is a striking admission from the same agency that maintains a 40,000-well inventory, the most water wells per capita of any county in California, with roughly 23,000 parcels relying on groundwater as their primary supply.

The disclosure paperwork closes part of that gap but not all of it. California sellers complete a Transfer Disclosure Statement and are required to disclose known water quality problems, system age, and maintenance history. Lenders add their own layer: FHA and VA loans typically require proof that well water meets EPA standards and flows at 3 to 5 gallons per minute. None of that is a county inspection. It is a private transaction requirement, which means the quality of your due diligence depends entirely on who you hire and what you ask for, not on a government stamp that already happened.

For a buyer touring a Sonoma Valley estate with mature vines and a decades-old well, that distinction is the whole ballgame. The well permit on file with the county tells you the well was built to code in the year it was drilled. It tells you nothing about whether the water is safe to drink this month.

Sonoma's soils, and why septic gets more scrutiny than most counties give it

If the well side of the ledger is quiet, the septic side has been anything but. Permit Sonoma is candid about why: the county's soils are, in its own words, notoriously poor for septic systems. That single fact shapes almost everything else in this section.

The county just finished a multi-year rewrite of its septic rulebook. The Board of Supervisors approved a revised Onsite Wastewater Treatment System Manual and Local Agency Management Program in August 2024, the North Coast Regional Water Quality Control Board sent back comments in March 2025, the county transmitted a revised version in December 2025, and the Regional Water Board formally approved the current OWTS Manual and LAMP in June 2026 under Resolution No. R1-2026-0022. That approval is two months old as of this writing. Any septic disclosure conversation you have this fall is happening under rules that didn't exist a year ago.

A few specifics matter if you are buying or selling in Sonoma Valley specifically rather than Sonoma County broadly. The manual includes special provisions for three watersheds the county has designated as impaired: the Russian River, the Petaluma River, and Sonoma Creek. The San Francisco Regional Water Board has adopted Total Maximum Daily Load action plans specifically for the Petaluma River and Sonoma Creek, and the county's OWTS Manual implements those plans directly. A parcel near Sonoma Creek carries a different septic conversation than one three miles away, because the manual's advanced protection requirements attach to the waterbody, not to the county as a whole.

The manual also finally addresses something Sonoma Valley's older properties actually have: cesspools. Cesspools are prohibited under state OWTS policy, and the county's new manual adds a conversion pathway that waives the typical site evaluation to encourage owners to remove them. If you are the legacy owner of a historic Sonoma Valley property that predates modern septic code, this is worth a call to Permit Sonoma before you list, not after an inspector finds it.

"Sonoma County's soils are notoriously poor for septic systems, so this is a sometimes challenging mission."

That line comes directly from Permit Sonoma's own description of its Well and Septic Division's work. It is not marketing language. It is the agency describing the terrain its own inspectors work in every day.

The monitoring program that just got smaller

One more shift is worth knowing about if you own, or are buying, a property with a non-standard septic system, meaning one with supplemental treatment beyond a standard tank and drainfield. The county's Operational Permit and Monitoring program, known as OPR, has historically required biannual self-monitoring reports and an easement recorded on the property allowing county staff to inspect the system.

Recent changes to state septic policy, combined with a vote by the Board of Supervisors, allowed Permit Sonoma to remove thousands of systems from that program entirely. If your property graduated out, you no longer file self-monitoring forms or pay annual fees, and the county no longer performs periodic inspections. The recorded easement may still sit on title even after graduation. Removing it requires a formal quit claim request and a fee, which stood at $388 under the county's 2024-2025 fee schedule. Worth checking before you assume the easement is gone simply because the monitoring requirement is.

What this means before you write the offer, or the listing

For buyers, the working list looks like this before you get too attached to the view:

• Confirm the well permit and completion report are on file with Permit Sonoma, and check whether a hydrogeologic report or Geotracker contamination search shows anything on the parcel.
• Ask for the static water level and the actual sustained yield in gallons per minute, not just "the well has never run dry."
• Order or request current lab results for bacteria, nitrate, and any relevant metals, since the county will not have tested any of this for you.
• Ask directly whether the septic system has ever been enrolled in the OPR program, and if so, whether it has graduated and what that means for the recorded easement.
• If the parcel sits near Sonoma Creek or another TMDL-listed waterbody, ask whether the septic system falls under the manual's special provisions.

For sellers, particularly those managing a legacy family property or an estate sale, the sequence matters as much as the substance. Order your well yield test now, while the dry season window is still open, rather than in October when shallow wells lose the option entirely. Pull your septic permit history before a buyer's inspector does. If a cesspool is part of the story, get ahead of the conversation with the county's new conversion pathway rather than letting it surface as a surprise during someone else's due diligence period.

Larger acreage and vineyard-adjacent parcels carry one more layer. Wells within the county's Public Trust Review Area that would push total groundwater use above two acre-feet per year require a discretionary review tied to the impact on nearby streamflow, since reduced flows can strand endangered Coho salmon in summer pools. If your property or the one you are considering irrigates at any real scale, that review is part of the timeline, not an afterthought.

None of this is a reason to walk away from a Sonoma Valley country property. It is a reason to treat the water and wastewater systems with the same seriousness the county does, which is considerable, and to build your timeline around the actual regulatory calendar rather than a generic escrow schedule borrowed from a suburban transaction.

Questions Sonoma Valley buyers and sellers ask us

Does the county test private well water when a home sells? No. Well water quality is not regulated by any government agency in California. Testing and disclosure are worked out between buyer and seller, typically through independent lab testing arranged during the inspection period.

What happens if a well fails the sustained-yield test during the dry season? For shallow wells, there is no extension past October 1. A failed or unfinished test may mean waiting for the next testing season, which can affect a seller's timeline more than the county's technical requirements themselves.

Do all septic systems in Sonoma County need annual monitoring? No. Only non-standard systems with supplemental treatment are enrolled in the county's OPR program, and recent changes have removed thousands of systems from that requirement. Standard systems were never part of it.

Does the new OWTS Manual affect a septic system that isn't being changed? According to Permit Sonoma, if no development is proposed, the revised manual has no impact on an existing, functioning system. It matters most when a system is failing, being repaired, or when new construction is planned.

Wells, septic, and title work on a country estate are rarely the romantic part of the search. They are the part that decides whether the romantic part closes on schedule. The Kathleen Leonard Team has spent years managing exactly this kind of Sonoma Valley transaction, from legacy family properties to acreage purchases that involve real water rights questions. If you are weighing a country property this season, on either side of the table, request a private Wine Country consultation and let's map the calendar before it maps you.