A wet basement always has a cause, and the right fix depends entirely on where the water comes from. Spend on the wrong method and you'll be doing it again.
Interior drainage
Interior drain tile + sump pump ($40–$100/linear ft plus $600–$2,000 for the pump) is the workhorse fix for water that reaches the basement through the wall–floor joint or up through the slab. A channel inside the perimeter collects the water and a sump pumps it out. Less disruptive than digging up the yard, and reliable for hydrostatic pressure. Interior sealant/coating ($3–$10/sq ft) only handles light surface dampness — not active water.
Exterior methods
Exterior excavation + membrane ($80–$200/linear ft) is the most thorough — and most expensive — option: dig down to the footing and apply a waterproof barrier so water never reaches the wall. An exterior French drain ($10–$100/linear ft) intercepts surface and groundwater out in the yard before it ever gets to the house.
Which to choose
Method ranges follow national aggregator data. See our methodology.