Condensation can build up inside a watch crystal whenever the watch is exposed to a lot of water, extreme fog, or humidity. Whenever the watch warranty is in place, most manufacturers recommend those who are familiar with the workings of the timepiece remove the condensation. However, if the warranty has expired, there are ways to remove the condensation on your own.
Remove the back of the watch carefully. It you still have the instructions that came with the timepiece, use those to ensure you don't damage the watch. Otherwise, choose jeweller sized tools to pry the back off the watch without fear of causing permanent damage.
Check to see if the seal between the watch fixtures and the casing is intact. If it has eroded or broken, it will need to be replaced in order to prevent the same type of thing from happening again in the future. However, be aware that not every watch has a seal so if you don't find one, just move on to the next step.
Check to see if water has built up inside the watch fixtures. Use a magnifying glass to do this in order to see the fixtures clearly. If moisture is obviously present, you will need to treat both the watch crystal and its fixtures for condensation.
Remove condensation from the watch crystal by wiping it clean with a lint-free cloth. Using the magnifying glass, check closely to make certain you have not smudged or streaked the crystal. If so, use a bit of glass cleaner on a cotton swab to clear up the problem. Then wipe dry again with the cloth.
Hold the watch carefully over the top of a hot lamp light bulb, if the moisture issue inside the fixtures is only mild or can't be determined. The heat from the bulb should remove any minor condensation within a few minutes without damaging watch parts.
Put both the watch crystal and fixture into direct sunlight if you are afraid of touching any of the watch's inner workings. Let it sit in place until you note that the moisture is gone by looking through the magnifying glass.
Use a hair dryer on low to medium heat setting to eliminate mild to medium condensation from either the watch crystal or the fixtures.
Check to see if the watch is working properly. Watch it for a couple of hours to make certain that it isn't losing time or otherwise malfunctioning. If so, try replacing the watch battery and then check it again. If the watch appears to be working properly, move on to the next step. If not, it may be necessary to take it to a jeweller for complete repair.
Replace the watch backing, making certain that it fits snuggly into place. If it does not, then your seal may not be in the correct position. Adjust it until the watch closes properly.
Check to make sure the crystal remains clear and the timepiece is functioning properly before snapping the watch back fully into place.
If your watch is under warranty, it is best to take it to a jeweller in order to prevent negating the warranty by attempting to fix it yourself. If the watch is expensive, it may be in your best interest to pay a jeweller to fix the problem than risking the loss of the watch. Use seals that are made specifically for your watch only. Otherwise, the backing may not close properly and more damage could result. If you don't have a new watch seal on hand, check with local jewellers to determine where one can be purchased. Watch batteries can be purchased at most discount department stores, battery stores, and jewellers. The higher the magnification of the magnifying glass, the better look you will get into your watch fixtures. If the watch doesn't begin working after the condensation is removed or if it slows or speeds up, even after the battery is changed, then take it to a jeweller to determine the problem.
Do not try to pry off the watch back with an improper tool life a knife. You could damage the watch, thus negating its warranty, or hurt yourself. Do not set the watch fixtures directly on top of the light bulb, as this could permanently damage the watch. Leave the watch out in the sun only for the amount of time necessary to remove the condensation; no longer. Do not use a hair dryer set on high to dry any part of the watch.