Water in the garage can mean a couple of things, from a big problem to a minor, quick fix. Big picture, it could be an issue with the foundation or a driveway draining towards, rather than away from, the garage. Waterproof paint on the walls or a french drain can solve some of these issues, though it will range in cost. On a smaller scale, it can mean that the bottom rubber of the garage door has a large tear or hole in it, allowing water to enter the garage and will simply need to be replaced.