French drain vs dry well: which one does your yard need?

A French drain is a trench of washed stone wrapped in filter fabric with a perforated pipe, laid with a steady fall. It collects water and carries it to the end of the pipe. A dry well is a buried chamber, either a pit of stone or a perforated basin, that holds water and lets it soak into the surrounding ground. One moves water, the other parks it.

So the first thing we look for on a walk is the outlet. Can the pipe run downhill and come out in daylight, on a slope or into a swale where the water can leave the property without bothering a neighbor or a road? If yes, the drain is usually the simpler and more reliable answer. If the lot is a bowl with no downhill side, the drain has nowhere to end, and a dry well becomes the candidate. Only then does the soil question decide it.

Pick the drain when water arrives slowly through the ground and a downhill route exists. The classic cases are a seep at the base of a slope, a soft strip on the uphill side of a patio, and a flat side yard between houses that stays wet for days after rain. A drain laid across the path of that water, uphill of the area you use, catches it before it gets there.

It also scales better with the weather. A drain does not fill up. As long as the outlet is clear and the fall is right, it keeps moving water through a long wet week. That matters here. At Westchester County Airport, 2023 to 2024 had 20 days of an inch or more of rain, against a ten season mean of 10 (NOAA daily data). A system sized for an average year gets tested in a year like that, and a pipe with a free outlet has no ceiling to hit.

A dry well fits one situation: a low spot with no outlet, where the soil below really does drain. Roof water from a downspout that has no place to go is the usual use. It collects the flow, holds it during the storm and lets it seep out afterward.

That is also where it fails here. A dry well needs two things, soil that accepts water and enough depth above the seasonal water table and bedrock for the water to go. County soil data says 84.5 percent of rated soil acres in Westchester have a seasonal water table within 36 inches or bedrock within 40 inches (USDA NRCS SSURGO, survey NY119). A well in soil like that fills and stays full, then overflows the next time it rains. The map is drawn at the scale of acres, not yards, so we do not trust it alone. We dig a test hole where the well would go, fill it with water and watch how fast it drops. A hole that is still full the next morning has answered the question, and the answer is no well.

A lot of yards that get a drain or a well needed neither. Go out during a steady rain, not after it. If water is running across the surface toward the house or a low spot, the cause is grade or roof water, and a pipe in the ground will not fix a slope pointed the wrong way. Regrading the strip beside the foundation, extending downspouts, or cutting a shallow swale is usually the smaller job.

Roof water is the other one to rule out. A downspout that empties at the foundation or into a bed can saturate a corner of the yard by itself. Moving that flow a few feet away often dries the spot, and our roof water and drainage guide covers how to check before winter. Tell us what you see on the estimate request: every rain, or only after the biggest storms. It changes how big the fix needs to be.

People searching dry well vs French drain cost usually expect the well to be the cheap one. It is not automatically. A well can be a smaller excavation, but a well that fails in tight soil is a repair you pay for twice. A drain with a downhill outlet is often the lower cost route because the outlet is free. What moves either number is the same set of things: run length and depth, ledge and roots, the outlet, and what has to be put back afterward. We break each one down in our French drain cost guide.

Whichever you are quoted, ask for the outlet or the well location and depth in writing, what stone and fabric go in, and what happens if ledge turns up. A quote that does not say is a guess.

Nelson walks the property, runs the water test with you if it is raining, digs a test hole where a well would go, and writes the scope after seeing the grade, the soil and the outlet options. Sometimes the recommendation is a drain, sometimes a well, sometimes a regrade and nothing buried. The visit is free.