Homeowner Guide

How Does a French Drain Actually Work?

"French drain" gets used loosely for a lot of drainage fixes, but the actual system is specific: a trench, a perforated pipe, and gravel, working together to move water below the surface instead of letting it pool on top. Understanding how it actually works helps explain why it solves some yard drainage problems and not others.

The Basic Mechanism

A French drain is a trench dug along the path water needs to travel, lined with gravel, with a perforated pipe running through it. Water in the soil enters through the pipe's perforations, travels along the pipe (which is sloped to move water in one direction), and discharges somewhere it won't cause a problem — a storm drain, a dry well, a daylight outlet at a lower point in the yard, or a similar safe exit point. The gravel around the pipe helps water reach the perforations quickly and keeps soil from clogging them over time.

What It's Actually Good For

French drains are the right tool specifically for subsurface water — water moving through the soil that's saturating a yard, pooling in a low spot, or seeping toward a foundation. They're not the right fix for every drainage problem: surface water that sheets across a yard during heavy rain is often better solved with regrading or a surface drain, and water actively entering a home needs its own targeted solution. Part of a real drainage assessment is figuring out which kind of water problem you actually have before recommending a French drain specifically.