tank leak

Is my tank leaking? Or just the humidity due to the tank? Under the table where the tank is put in, the tiles is always slightly wet, wet like when you blow against your window and it fogs and you touch it, thats what it feels.

How long do glass aquarium last before you proactively take them out of service or replace them to avoid a catastrophy or leak? Obviously, there are levels of quality that could affect this number. So perhaps a high/low answer? Anyone with real experience? Any manufacturers with tested and...