water source; source of a river; fountainhead
Refers to the origin of a river or a supply of water. Also used figuratively for the origin of something, though less common.
この川の水源は山奥にある。
The source of this river is deep in the mountains.
Protecting water sources is important.
This forest is protected in order to preserve the town's water source.
The water source dried up because of the long drought.
The villagers dug a well to secure a new water source.
The factory's wastewater had polluted the water source.