What does "begins to water" mean?

My mouth waters just before I eat something delicious.

My mouth is having an involuntary biological response to the stimulus of food. The response is the production of saliva in the mouth, in order to aid digestion.

The "water" in the expression "your mouth begins to water" is a reference to saliva in the mouth.

The expression means that you expect to eat something delicious

Also, this is typically a metaphorical expression, that is, your saliva doesn't necessary start to gush in anticipation of something. Even when you're in the presence of your favorite food, your mouth doesn't really start to drool. All this is conveying is an eager anticipation of something, for example:

"My mouth began to water as I thought about the Thanksgiving spread my aunt a

Carter LeeI want to know the meaning of "begins to water" in the sentence.

= Begins to salivate.

Saliva is the liquid in your mouth that helps you to eat food. Salivate is the process where your salivation glands produce this liquid.

If you are hungry and smell some really delicious food, you will salivate. Your mouth waters.