The name water becomes fragrant is not an idiom. There is a saying that "when it meets water, it becomes fragrant tea", which means that when it meets water, it is probably the name of a tea shop, or the owner of this tea shop is named Shuicheng, and the shop is named after a person. It may also be the brand or trademark name of a kind of fragrant tea.
Xiangming is another name for fragrant tea.