What's the difference between a French drain and a dry well?

A French drain MOVES water: it's a gravel-filled trench with a perforated pipe that collects water along its length and carries it somewhere better. A dry well STORES water: it's a buried chamber or stone pit that takes a rush of water - like a roof downspout in a storm - holds it, and lets it soak slowly into the surrounding soil. Different jobs. Many yards need both, with the French drain emptying into the dry well.

Does a French drain need somewhere to drain to?

Yes - always. A French drain is a delivery system, not a destination. The water has to end up somewhere: daylight at a lower spot on the property, a dry well, or an approved connection. French drains that 'stopped working' were usually built without a real outlet, so the water just sat in the trench.

Which costs less - a French drain or a dry well?

It depends on the yard. A dry well catching one downspout is often the smaller project; a French drain's cost scales with how long and deep the trench runs and what's in the way. Since many fixes combine the two, the honest answer comes from a site visit - we give a free written estimate with the real number either way.

How long do French drains and dry wells last?

Built right - washed stone, filter fabric, proper pipe, a real outlet - both should serve for decades. The failures we get called to fix almost always come down to missing fabric (the system silts up), crushed or bellied pipe, or no outlet. Keeping gutters clean upstream is most of the maintenance.

French Drain vs. Dry Well: Which Does Your Yard Need?

Q: Do dry wells work in clay soil?

They can - if they're sized for it. Clay drains slowly, so a dry well in a clay-heavy Greater Boston yard has to be bigger, deeper, or placed where the soil percolates better, which is why testing how fast your soil actually absorbs water comes before sizing the well. An undersized dry well in clay fills up in the first hour of a storm and acts like it isn't there.

Short answer: they do different jobs. A French drain moves water — it collects it along a soggy stretch and carries it somewhere better. A dry well stores water — it swallows a sudden rush (like a roof downspout in a storm) and lets it soak into the ground slowly. If your problem is water spread across the yard, think French drain. If it's a concentrated gush with nowhere to go, think dry well. And in a lot of Greater Boston yards, the right answer is both, working together — the drain collects, the well disposes.

Homeowners ask us this one constantly — usually standing in a wet lawn in Somerville or Medford, phone in hand, having just read three contradictory articles. Here's the honest version: it's not a versus at all. They're two tools that solve two halves of the same problem, and picking the right one starts with asking what your water is doing.

What a French drain is (and what it's actually for)

A French drain is a trench filled with washed stone, wrapped in filter fabric, with a perforated pipe at the bottom, pitched so water flows where you want it. Water seeping through your yard finds the trench, drops into the pipe, and rides it away.

It shines when the water is spread out: a stripe of lawn that stays spongy for days, water creeping along a foundation, a slope that sheets runoff at your patio, the neighbor's uphill lot draining into yours. The drain intercepts water along its whole length — that's its superpower.

The catch: a French drain needs a destination. It's a delivery truck, not a warehouse. The water has to daylight at a lower grade, tie into an approved outlet — or empty into a dry well. Half the "failed" French drains we dig up were built without a real outlet. The water rode the pipe to the end, found nowhere to go, and sat.

What a dry well is (and what it's actually for)

A dry well is buried storage: a perforated chamber or stone-filled pit, wrapped in fabric, that accepts a surge of water, holds it, and lets it seep into the surrounding soil over hours instead of flooding your yard in minutes.

It shines when the water is concentrated: a downspout dumping a whole roof's worth of storm onto one corner, a sump pump discharge, the end of — you guessed it — a French drain. One inch of rain on an average roof is well over a thousand gallons, all arriving at once. A dry well is the shock absorber.

The catch: a dry well is only as good as the soil around it. It disposes of water by soaking it into the ground — and Greater Boston's clay-heavy soil drinks slowly. That's why sizing matters more than anything: we test how fast your soil actually absorbs water before choosing the well's size and location. An undersized dry well in clay fills in the first hour of a nor'easter and then it's just an expensive hole.

The quick decision guide

Soggy area, water spread along a stretch of yard or foundation → French drain
One gushing source (downspout, sump line) and decent soil → dry well
Yard has a lower spot where water can exit to daylight → French drain alone may do it
Flat urban lot, no lower exit, water spread around → French drain into a dry well — the classic Somerville/Cambridge combination
Heavy clay everywhere → whatever we build gets sized for slow soil, or we look at permeable surfaces that stop the runoff at the source

Why they're usually teammates, not rivals

On flat, tight lots — which describes most of Somerville, Cambridge, and half of Medford — there's no downhill to send water to. So the system that actually works is: French drain collects the spread-out water, pitches it to a dry well sized for your soil, and the well disposes of it underground. Collection plus disposal. That's not upselling; it's plumbing logic. Water needs a path and a destination, and each tool is only half the sentence.

What makes either one last 30 years (or fail in 3)

Same story as patios: what's buried decides everything. Washed stone (not fines that clog), real filter fabric around everything (or the system silts shut), pipe with the right slope that won't belly or crush, and a genuine outlet. As an NDS Certified Professional Drainage Contractor, this is the engineering half of our business — and the reason our drainage work comes with the same built-to-last attitude as our patios. Upstream maintenance is simple: keep the gutters clean, and don't let landscape fabric's enemies — silt and roots — get a head start.

Common questions

What's the real difference in one sentence?

A French drain moves water from where it's causing trouble; a dry well swallows and disposes of it. Path versus destination.

Do dry wells work in clay soil?

Sized right, yes. Clay absorbs slowly, so the well gets bigger, deeper, or relocated to better-draining soil — which is why we test percolation before we dig.

Does a French drain need an exit?

Always. Daylight, an approved outlet, or a dry well. No exit, no function.

Which one costs less?

Depends on the yard: a one-downspout dry well is often the smaller job; a French drain scales with trench length and depth. We'll tell you which your yard needs — free on-site look, written estimate, real number.

Standing water that won't quit?

We'll come out, find where the water's coming from and where it can go, and put the fix in writing — free, no pressure.

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