When I think about it, it makes my mouth water.想起它我都会流口水。

固定表达make one's mouth water，就相当于汉语中的“使……流口水”，是个不太正式、偏于口语的用法。
　　例句：
　　The roast duck that restaurant serves is my favorite dish. Every time I think about it, it makes my mouth water.
　　我最喜欢吃那个饭馆的烤鸭。每当我想起它我就会流口水。