My watch says '30 meters water resistant' is less than a year old,
doesn't appear damaged but still has moisture inside, what's the deal?

This is one of the most important (and often misunderstood)
concepts.  The principle of water resistance to 30m, 100m, etc is
simple, in theory anyway. It's easy to understand this way; if
your watch says '30 meter water resistant' your watch is
resistant to the
static (or stationary) pressure of 30 meters (or 100
feet) of water.  If you were on a boat and lowered your watch
into the water 30 meters, it should resist the pressure at that
depth and remain dry inside.  Simple, right?  Now take an
ordinary garden hose and spray the crown with the strongest
stream of water (
note: if you do try this we will not be responsible!!),
what happens?  Your water resistant watch is now full of
water, but how?  Water resistance is measured with
(stationary) pressure
when tested the watch is put into a
chamber and the pressure is raised to the intended depth.  
When the hose was turned on the water had
dynamic pressure
(or force), this force was greater than the pressure the gaskets
could resist.  The water resistance table are listed later.  In
short, the higher the water resistance rating the more
force it
will take to get water into your watch.  
30 meters use caution,
200 meters dive on in.