noun
source of a spring; springhead
Literal source of water, such as a spring or fountainhead. Often used in geographical or natural contexts.
この川の源泉は山の中にある。
The source of this river is in the mountains.
読書は知識の源泉だ。
Reading is a source of knowledge.
彼の収入の源泉は投資だ。
His source of income is investments.