make one's mouth water, to

to make someone hungry (for something); to cause saliva to flow in someone's mouth. That beautiful salad makes my mouth water. Talking about food makes my mouth water.

Cause one to eagerly anticipate or long for something, as in Those travel folders about Nepal make my mouth water. This metaphoric term alludes to salivating when one anticipates food and has been used figuratively since the mid-1600s, whether it refers to food, as in The sight of that chocolate cake made her mouth water, or not.

To make someone long for or desire something; to arouse eager anticipation. The term, which alludes to salivating in anticipation of food, transferred the phenomenon to other human desires early on. Richard Eden used the term in writing of cannibals anticipating their prey (The Decades of the New Worlde, 1555). By 1663, when Samuel Butler used it in Hudibras, the term was purely figurative, as it still is, even when it refers to food.