A watery mouth can be caused by many conditions including: salivary gland complications, upper respiratory tract infections or allergies, the hormonal changes of pregnancy, stomatitis, reactions to anti-epileptic medications and gastro-esophageal reflux disease (GERD), according to Medical Base. It can also simply be the body's reaction to the anticipation of eating food or drinking liquids.
A watery mouth is caused by an excess of saliva produced by the salivary glands. Normally, the salivary glands constantly produce small amounts of saliva throughout the day to keep the oral cavity moist, keep bacteria in check and assist with digestion; the body reacts by swallowing periodically. Sometimes the salivary glands produce too much saliva, resulting in difficulty swallowing or speaking, drooling or trouble sleeping. While not typically serious or permanent, excessive production of saliva can cause embarrassment and anxiety. Those suffering from GERD are especially susceptible, as the digestive acids present in the mouth can cause the salivary glands to produce as much as two teaspoons of saliva every minute.
Watery mouth usually goes away on its own. In prolonged or especially severe cases, it may be a symptom of a more serious underlying condition such as a sinus infection or other illness.