What Yard Drainage Costs on Long Island
French drains, dry wells and regrading — real Suffolk County numbers, and an honest answer about which one your property actually needs.
COST GUIDE | Hampton Dreamscapes | Updated September 2026
COST GUIDE
Most People Buy the Wrong Drainage System
Drainage is the single most commonly mis-sold service in Long Island landscaping. A homeowner has standing water, calls a contractor, and gets quoted a French drain — because a French drain is what contractors install. Sometimes it is right. Often the problem was grade, and a fraction of the money spent on regrading would have solved it permanently.
In Suffolk County, exterior French drain systems run $30 to $47 per linear foot installed. A typical 60 to 100 foot run therefore lands between $1,800 and $4,700, reaching $7,000 or more on complex layouts. Interior basement perimeter systems are a different animal at $74 to $89 per linear foot, because of the concrete cutting and restoration involved.
Before spending any of that, it is worth knowing which problem you actually have.
On flat ground, moving the water is cheaper than catching it. Grade first, pipe second.
THE BREAKDOWN
What Each System Costs, and What It Is Actually For
These solve different problems. Buying the wrong one is how people end up paying twice.
Regrading — often under $2,000
Establishing real fall away from the house. On flat South Shore lots this is frequently the entire fix, and it is the first thing that should be assessed. Unglamorous and very effective.
Exterior French drain — $30 to $47 / lin ft
A perforated pipe in a gravel trench, intercepting subsurface water and moving it somewhere useful. Right for persistent wet areas and slopes. Useless if there is nowhere for the water to go.
Dry well — $700 to $4,000
A buried chamber that holds water and lets it infiltrate. Excellent where soil below is unsaturated. Worthless where the water table is already high — which is most of Shirley, Mastic Beach and Water Mill.
Catch basins and surface drains
Typically $400 to $1,200 per basin installed and tied in. For collecting surface water at a defined low point. Only as good as whatever they drain into.
Downspout tie-ins — $300 to $900 each
Routing roof water away from the foundation instead of dumping it beside the wall. Frequently the cheapest meaningful improvement available on an older house.
Interior perimeter — $74 to $89 / lin ft
Inside the basement, under the slab, tied to a sump. Costs more because of concrete cutting and restoration. This is waterproofing rather than landscaping, and it is a last resort, not a first one.
AT A GLANCE
The Short Version
A French drain is probably right if:
- Water is coming from uphill or from a neighbouring property
- There is a persistently wet band across the yard
- You have somewhere lower for the water to actually discharge
- The problem persists even in a normal rainfall year
A French drain is probably the wrong answer if:
- Your water table is at or near the surface
- The ground is flat with no legal discharge point
- The grade slopes back toward the house
- Water only appears in exceptional storms
On a low, flat Suffolk County lot the honest answer is frequently regrading plus a modest surface system, not a long buried pipe. Any contractor who quotes drainage without digging a test hole first is guessing with your money.
Drainage Questions We Get Constantly
Why did my dry well stop working after a year?
It probably never worked. A dry well only functions if there is unsaturated soil beneath it to accept water. Where the seasonal water table is high — much of the South Shore, and Water Mill on the East End — the well fills and stays full. This is the most common drainage failure we are called out to.
Can I just drain water into the street?
Usually not legally, and in wetland and watershed areas definitely not. Most municipalities require stormwater to be managed on your own property, and near the Carmans River, the Forge River or the East End ponds it is enforced. Designing for infiltration is the compliant answer and the better one.
How long does drainage work take?
Most residential jobs run one to three days. Regrading alone is often a single day. The variable is access and how much material has to come out and go back in.
Will drainage work damage my lawn?
Temporarily, yes — there is no way to trench without disturbing turf. Restoration is part of the job and should be in the quote. Ask specifically whether it is, because that is a common place for a low quote to hide.
Is it worth doing before I install a patio?
Absolutely, and it costs far less done at the same time. Retrofitting drainage under a finished patio means taking the patio up. If there is any question about water on the site, resolve it before the hardscape goes down.
Want a Straight Answer About Your Property?
Free estimate, no pressure, and an honest number. We work from Patchogue to Montauk and Shelter Island.