Garage doors are designed to sit flat on the ground. A new, properly installed and adjusted garage door normally keeps most water out, however, heavy rains, blowing rains, or driveways that slope down to the garage door will sometimes allow water to seep in.
If you have water entering your garage, you could need new seals or the garage door needs to be adjusted.
If those remedies don’t work, it might be time to consider a new door.