There's no guarantee that the condensation would show up on it's own, but if you warm the watch with a hairdryer and then place a drop of cold water on the crystal, any moisture inside will condense on the insde of the crystal under the drop. You have to get the watch pretty warm (not so warm that you can't still hold it in your hand), but this test is very effective.
I believe all recent/modern standard Speedmasters have a water resistance rating of 50 meters.
