飲水思源

From "Tune in the Key of Zhǐ" (徵調曲) written by Yu Xin (庾信) during the Northern and Southern dynasties:

落其實者思其樹；飲其流者懷其源。 [Classical Chinese, trad.]

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落其实者思其树；饮其流者怀其源。 [Classical Chinese, simp.]

Luò qí shí zhě sī qí shù; yǐn qí liú zhě huái qí yuán. [Pinyin]

When you eat the fruit, remember the trees that produced them; when you drink water, think of its source.

i.e. remember where and how the fruit/water came from. Don’t just be thankful for the fruit/water. The idiom makes use of the latter half: be thankful for all the elements and processes (both past and present) that allowed you to enjoy that humble cup of water.

飲水思源

1. to remember where one's happiness comes from; to not forget one's roots or heritage

• → Vietnamese: uống nước nhớ nguồn (calque)