Short answer
A French drain intercepts water in the yard before it reaches your foundation; a sump pump removes water that's already made it into your basement or crawl space. They address different points in the same water path, which is why many properly waterproofed homes have both — the French drain reduces how much water ever becomes the sump pump's problem, and the sump pump handles whatever still gets through.
What each one is actually doing
A French drain is a gravel-filled trench with a perforated pipe, positioned to catch water moving through the soil and redirect it away from your house before it ever reaches the foundation wall. A sump pump, by contrast, sits inside a basin in your basement or crawl space floor and removes water that's already arrived, pumping it out and away through a discharge line.
When a French drain alone is enough
If the water problem is really a yard problem — pooling near the foundation, a soggy patch that never fully dries, a downspout dumping water right next to the house — and it hasn't yet resulted in actual basement water, a French drain (sometimes paired with regrading) can resolve it on its own.
When you need the sump pump too
If water is already getting into the basement through the cove joint, a crack, or a block wall, a French drain outside won't remove water that's already inside — that's specifically the sump pump's job, usually paired with an interior perimeter drain that channels the water to the basin in the first place. For most homes with an active water problem, addressing just one side without the other leaves a gap: exterior drainage without an interior system doesn't help water already inside, and a sump pump without addressing the source keeps fighting the same volume of water indefinitely.
Frequently asked questions
Combined installs are typically more efficient than doing them as two separate projects later, since some of the labor and access work overlaps.
Only if it fully prevents water from ever reaching the foundation, which isn't guaranteed on flatter lots or during unusually heavy rain — most homes benefit from having the sump pump as a backstop regardless.
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