Where Does French Drain Water Go? Discharge Options and Local Rules

A French drain collects water. It doesn’t make it disappear. Every foot of gravel and perforated pipe in the ground still has to end somewhere, and where that “somewhere” is turns out to matter — legally, not just practically. Send it to the wrong place and you can end up with a notice from the city, a dispute with a neighbor, or a drain that quietly stops working. Here’s what the water is actually allowed to do once it leaves the trench.

Why “just send it toward the fence line” isn’t really an option

The simplest-sounding fix — run the pipe to the low side of the yard and let gravity do the rest — is legal in principle, but it comes with a real limit. California follows what courts call a modified civil-law “reasonable use” rule for surface water between neighboring properties. The California Supreme Court’s decision in Keys v. Romley lays out the standard: an upper (higher-elevation) landowner is generally entitled to let water drain as it naturally would, but is liable for damage caused by discharging it in an “unnatural manner.” Courts weigh the amount of harm caused, how foreseeable that harm was, and whether the benefit to the upper owner’s use of their land outweighs the burden placed on the lower owner.

In plain terms: a French drain that quietly daylights at your own low corner and soaks into your own planting bed is a very different thing, legally, than a pipe that collects water from a wide area and shoots it in a concentrated stream onto a neighbor’s lawn or against their fence. The first is ordinary use of your land. The second is exactly the kind of “concentrate, accelerate or artificially increase” drainage that Keys v. Romley and later cases hold an upper owner responsible for.

What federal rules actually say about this water

Municipal storm drain systems (MS4s) operate under federal Clean Water Act permits that require cities to prohibit “illicit discharges” — EPA defines an illicit discharge as any discharge to the storm drain system that isn’t composed entirely of stormwater. That’s the source of the simple rule most Bay Area clean-water programs post for residents: Contra Costa Clean Water Program’s public guidance states plainly that only rainwater is allowed to flow freely into a storm drain, with wash water, sediment and similar pollutants prohibited.

What’s less publicized is EPA’s own list of discharges that don’t have to be treated as illicit in the first place — and it reads like a description of a French drain: foundation drains, footing drains, uncontaminated groundwater infiltration, rising ground water, uncontaminated pumped groundwater, water from crawl space pumps, and landscape irrigation water are all on the federal exempted-category list. The clean groundwater a well-built French drain carries is generally the kind of water the federal rule doesn’t treat as a pollution problem.

That federal exemption answers one question — is the water itself acceptable — but not the other one: whether your city lets you physically tie a private pipe into its storm drain system. That’s a separate, local permission.

The storm drain: usually allowed, always a permit question

City of Concord’s own description of its encroachment permit process is typical of how Bay Area cities frame this: an encroachment permit is required for anyone who proposes to do work in, or connect to, the public right-of-way or a water course — which is exactly what tying a private drain line into the public storm system involves. Cities vary in how closely they police this for a small residential French drain, but “it’s probably fine” isn’t the same as “it’s permitted,” and an unpermitted connection discovered later (often during a resale inspection or a street project) is a more expensive problem than a phone call would have been.

Dry wells: the option with the most fine print

A dry well — a gravel-filled pit that lets water soak into deeper, more permeable soil — sounds like the self-contained option that avoids the neighbor question and the permit question both. In practice it has more regulation attached to it than either of the other two choices, not less.

Federally, a dry well counts as a Class V injection well under the EPA’s Underground Injection Control program (a “conduit for non-hazardous fluids deeper than it is wide”). EPA guidance specifically calls out dry wells serving lots other than single-family homes as subject to registration requirements; a single-family residential dry well generally falls outside that individual registration mandate. That’s the good news. Separately, though, California’s State and Regional Water Quality Control Boards have their own authority under the Porter-Cologne Water Quality Control Act to require a report of discharge for an injection well and to apply the state’s Anti-Degradation Policy, which protects high-quality groundwater from unnecessary degradation. The Bay Area’s own Regional Water Quality Control Board restricted dry well use back in 1951 specifically to protect groundwater quality, and the San Francisco Public Utilities Commission now steers people toward wide, shallow infiltration basins instead of the classic deep, narrow dry well.

Soil is the other problem. Design standards used in other parts of California — Los Angeles and San Diego’s stormwater permits, Placer County’s LID manual — generally call dry wells unsuitable in soil with more than 30% clay. The USDA’s official soil survey for the Diablo clay series, common across Alameda and Contra Costa counties, documents 45–60% clay through most soil horizons. That’s not a Bay Area-specific dry well standard (none of the sources above write one), but it’s a straightforward reason a dry well that works well in sandy soil elsewhere in the state can simply refuse to drain on a typical inland Bay Area clay lot.

Confirming your city’s rule before you dig

1. Step 1Check your city’s public works or engineering pageSearch for “encroachment permit” and “storm drain connection” on your city’s site, or call the permit counter directly.
2. Step 2Ask the direct question about a storm drain tie-inConfirm whether a private drain connection to the public storm system needs a permit and an inspected point of connection — in most Bay Area cities, it does.
3. Step 3Ask about dry well rules if you’re considering oneLocal practice on dry wells varies by city and county far more than storm drain rules do; don’t assume what’s allowed one town over applies at your address.
4. Step 4Confirm a daylight outlet stays on your own lotWalk the discharge point with the actual grading in mind — not just where the pipe is shortest, but where the water genuinely ends up once it leaves the pipe.

Before you pick a discharge point

Questions homeowners ask

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