Don't be afraid to swallow some seawater. Clench the mouthpiece between your teeth and "Grin"..some seawater will enter your mouth and help relieve the dryness.

The dry mouth or cottonmouth that you are experiencing is commonly caused by the air that is in the scuba cylinder. The air has the moisture pulled out of it during the filtering process during the filling. Sometimes just the act of swallowing can help. If you just started scuba class then you have probably already learned how to take your regulator out of your mouth and replace it. Taking some water into your mouth and swishing it around helps while the regulator is out of your mouth. Moving your tongue along the roof of your mouth can also help to activate your salivary glands as well. Being hydrated to begin with will also help. drink water before class and avoid liquids with caffeine which can add to dehydration. I have also used lemon drops (a hard candy) prior to diving which stimulates the salivary glands. This is especially good after diving as well. Another reason for the dry mouth could be attributed to the simple fact that you are "new" at diving. Beginning students have a tendancy to breath air from the cylinder faster than those that are more experienced or "comfortable". Breathing the dry air faster will dry out the mouth faster.