My watch has moisture under the crystal  (water damage)

People need water to survive.  Watches do not.  Water can
enter a watch in a number of ways.  First, the crystal may be
cracked or chipped around the edge, the crystal gasket might
be damaged, older plastic crystals shrink slightly or develop
tiny cracks that run around the base of them.  The gaskets
around the crown might be damaged due to age or chemical
breakdown.  If you have a chronograph watch, you may
have dirt or grit under the buttons which, once it get in,
allows moisture to get in.  Also, the back gasket will become
brittle over time and exposure to sweat, body oils, lotions,
etc.  One very important thing to remember is:
resistance is a condition, it is not permanent!
 Just because
your watch was water resistant six years ago when it was
new and has never been opened doesn't mean it is
still water
resistant!  Your gaskets should be checked and replaced every
two years (or every battery change) on watches that are not
normally subject to immersion.  On sport watches that see a
lot of wear and tear (sand, salt water, dirt, etc) or if you are a
diver and use your watch as a vital part of your equipment,
you should have your gaskets replaced and pressure tested
every year.