There are many potential signs of water infiltration and water damage; which ones will appear in your house largely depends on where the humidity is coming in. For example, if you have water infiltrating through a wall into a well-ventilated room, the first telltale sign you see will probably be strange stains appearing on the wall. Maybe even some visible dampness depending on the amount.
When the humidity is flowing into a closed space like a bathroom or a basement, however, you’ll often smell it before any visible signs appear. Humidity doesn’t quite have a smell, but you can often feel how damp the air is in your nose and on your skin. And the mold that often follows a humidity built up does have a distinct smell. It smells like musty, stale air.
At any rate, if you fear your house may have a humidity problem, the best thing to do is to call a professional inspection. Mold removal companies and damp proofing companies Kent often offer inspection services, as this website shows. A professional house inspector should also be able to help you spot humidity issues.