Where does the water in a river come from?

Question

I would guess from mountain water runoff and/or from aquifers, but a cite to a more substantial answer, something... Discovery Channel-worthy would be appreciated!

Answer 1

It all comes from rain and snow. water seeps into the ground and any that is not absorbed runs off into the groundwater system. the groundwater will flow downhill until it intersects with the surcase and that will create a stream, which will flow into a river.

Answer 2

Ultimately it comes from the sea, (by evaporation),
via rain, (by condensation), via run-off, (streams,
ground, sewers etc.), to the river.