The agency owns the public sewer main in the street. You own the lateral — the private pipe running from your house out to that main — and that is the section that blocks, cracks, takes on roots and costs money. That division is close to universal across Sonoma and Marin. What differs sharply, and what catches people out, is which agency owns the main on your street, and whether that agency also regulates your private lateral through an inspection ordinance.
The general rule
Public main: the district or city. Private lateral: the property owner, all the way to the connection.
Sonoma Water's sanitation code puts it plainly for the systems it covers — each living unit, commercial unit or agricultural enterprise must have its own sewer lateral. The lateral is a property asset, not a utility asset.
That is why a blockage in your front yard is your bill and a blockage under the street usually is not, and why a camera inspection matters: it establishes which side of the line the fault is actually on before anyone starts digging.
Which agency owns the main where you are?
In Sonoma County, incorporated cities generally run their own systems:
- Santa Rosa, Sebastopol, Windsor, Cotati, Rohnert Park, Healdsburg, Cloverdale — city departments handle both water and sewer
- Sonoma — the City supplies water, but sewer comes from the Sonoma Valley County Sanitation District, a separate body covering the wider valley
- Glen Ellen — Valley of the Moon Water District for water, Sonoma Valley County Sanitation District for sewer where available, septic where not
- Larkfield-Wikiup — the Airport/Larkfield/Wikiup Sanitation Zone
- Penngrove — the Penngrove Sanitation Zone
- Guerneville — the Russian River County Sanitation Zone, whose boundary broadly follows the urban service area
- Bodega Bay — the Bodega Bay Public Utility District supplies both water and sewer
Marin is more fragmented still. San Rafael is split by a hill: Central San Rafael, generally south from the top of Puerto Suello Hill, is San Rafael Sanitation District; north of it — Terra Linda, Marinwood, Lucas Valley, Santa Venetia — is Las Gallinas Valley Sanitary District. Two San Rafael addresses a mile apart can have different sewer agencies.
Where the district also regulates your lateral
This is the part that surprises Sonoma County owners who move to Marin, and vice versa.
Several Marin districts run private lateral programmes that require you to inspect and, if necessary, repair the lateral at defined trigger points:
- Ross Valley Sanitary District (Fairfax, Ross, San Anselmo, and Larkspur parcels it serves) — sale, a remodel over $75,000, or a remodel adding a bathroom
- Sanitary District No. 2 (Corte Madera, Belvedere) — title transfer plus six other triggers
- Sanitary District No. 5 (Tiburon area) — purchase or sale, and $50,000 of work cumulatively over three years
- Sausalito–Marin City Sanitary District — transfer, change of customer, work over $50,000, change of use, and a standing rule if the lateral has not been inspected in ten years
In Sonoma Valley, the ordinance allows the district to require inspection of any side sewer 30 years or older connected to the public sewer — an age trigger rather than a sale trigger.
For Santa Rosa, Windsor, Healdsburg, Cotati and Rohnert Park, we could not document a private lateral inspection or point-of-sale requirement in their published material. That is not proof none exists, and the city is the right place to confirm before a sale.
Why the treatment agency is not the answer
Central Marin Sanitation Agency is the name most residents in central Marin recognise, and Sewerage Agency of Southern Marin serves the same role further south. Both are regional treatment plants. Neither administers private lateral programmes.
Getting this wrong sends people to the wrong office. Compliance goes through the district that serves the parcel.
Related reading
Frequently asked questions
Where exactly does my responsibility end? Generally at the connection to the public main, which means the lateral under your yard and often under the sidewalk or part of the street is still yours. The exact demarcation is set by the serving agency, so confirm it for your parcel rather than assuming the property line.
Does the district repair the main for free? Maintaining the public main is the agency's job. That does not extend to your lateral, even where it runs under public ground.
How do I find out which district serves me? By address, through the agency or the county, rather than by town name. Sewer service boundaries do not follow municipal boundaries in either county.
Can the district make me inspect a lateral I am not selling? In some places, yes. Sausalito–Marin City has a ten-year inspection rule independent of any transaction, and Sonoma Valley's ordinance uses lateral age as a trigger.