If the smell or sight of food makes your mouth water, it makes you want to eat it.

For example, the smell of that bacon cooking is making my mouth water.

The roasting turkey made our mouths water.

Just the thought of having a big seafood dinner tonight makes my mouth water.

However, make your mouth water can also figuratively mean to make something seem very attractive or appealing, not just food, as in, for example:

“The travel brochures made my mouth water,” implying a strong desire to go on the trip. 

Here are some other meanings and examples:

1-To be very attractive or appealing:

The thought of a vacation made his mouth water.

The offer of a raise made her mouth water. 

2-To excite a desire or appetite for something:

The description of the new car made his mouth water.

The prospect of a new job made her mouth water.

3-To make someone want something very much:

The thought of a new phone made his mouth water.

Just thinking about the concert made my mouth water.

Tradução: dar água na boca.