We could construct a mechanism to fully funnel the water down a tube or chute to the bottom of the mountain, then transport back to the top via pumps or buckets. However, this will require an intelligently designed and employed mechanism to do so...
Or the SUN COULD SHINE and evaporate the water, putting it back on mountaintops all over the place. That's how rivers run today. THE SUN IS SHINING. Go out and look for yourself.
Ever notice when the sun shines down on cockroaches, they scatter?
Remind you of anyone?
Maybe he lives underground.