Installing an interior drainage system gets the water out but doesn’t waterproof the walls. For that, you need an exterior system: a French drain to relieve hydrostatic pressure and exterior waterproofing to protect the foundation.

It’s a big job that requires excavating around the house, but it may be the best solution if you have a foundation with numerous gaps. It also keeps the mess and water outside, which may be the best choice if you don’t want to tear up a finished basement.

The downside, besides a price tag that can reach $20,000, is that your yard takes a beating, and you may need to remove decks or walkways.