Have you ever noticed how all conference organizers always put out a jug of water and a glass for the speakers?
Do not be tempted to drink it, unless it is really necessary. Having a dry mouth is one of the normal signs of nervous tension, but if you drink the water, you will find that your mouth tends to get dryer and then you will want to drink more and more. You are better to leave it to your body’s natural reaction to a dry mouth, which is to generate more saliva than to wash any saliva that is there, by drinking the water.
Sucking a mint before your presentation will help generate the saliva you need to avoid a dry mouth, and is far more effective than drinking the water. Alternatively, you can gently bite the inside of your cheeks, which will also make you salivate.
It is of course wise to have a drink to hand in case you start coughing or to act as a temporary diversion while you gather your thoughts to answer a question.
All the best