With the summer months now upon us, and all of the summertime activities that come with, there is no doubt that your favorite timepiece, or timepieces, will be subject to wide variances in temperature and conditions. From the pool, to the ocean, to ambient high temperatures regularly in the 90's, if not approaching triple digits, and high dew points to go along with the high temperatures, to air conditioning, these extremes and variances in conditions can cause your timepiece to develop the dreaded foggy crystal.
Obviously, the best way to prevent moisture from entering your timepiece is to make sure the crown is properly secure prior to having your timepiece near water of any kind, or not wearing your watch near water to begin with. A foggy dial caused by water inside the timepiece may be the least of your worries, as water can severly damage the inner-mechanics of your timepiece. I would recommend having your watch serviced at a trusted jeweler following any water breach.
A foggy dial caused by a drastic temperature variance is fairly easy to rectify. To start, I recommend pulling out the crown to the 2nd position, normally the position you would use to set your watch. I feel this facilitates more air flow into your timepiece to assist the "drying" out process. The second step, place your timepiece in an area where the dial can receive direct sunlight. Nothing like using the help of powerful sun rays to give your watch an assist. This process should help in ridding your crystal of fog within a day or two. Throwing the timepiece in a bowl of uncooked minute rice can also help draw moisture from your timepiece if the aforementioned steps don't bare positve results.