Poets use the flow of water as a metaphor for the past and old affection to express their sadness and sorrow, which reflects their nostalgia for past lives.

 

In Li Bai's "Farewell to My Lover", the phrase "the water is non-retractable, the clouds are hard to find again" compares water to lost emotions, depicting the tragic scene after separation. This means the past days of loving each other are as non-retractable as water poured on the ground, as difficult to retrieve as the floating clouds that drift away, which shows the story protagonist's longing and pain for his lost love.

 

In Du Fu's "Twenty Miscellaneous Poems from Qin Zhou", the line "The clear Wei is merciless, and when I am worried about leaving Chang An for the west, you are flowing to the east" means that the Wei water is really merciless. The poet uses the eastward flow of the Wei water to contrast with his own westward journey as if the Wei water is totally unconcerned with his own suffering. By personifying the water, the poet expresses his nostalgia for Chang An and his sorrow for leaving the city.