John Gill Commentary Psalms 78:16

"He brought streams also out of the rock, And caused waters to run down like rivers." — Psalms 78:16 (ASV)

He brought streams also out of the rock
Which is expressed in the singular number, as also in (Psalms 78:20), because the children of Israel were not come to Kadesh, and the second rock was not smitten when they lusted after flesh, and murmured against God, and tempted him, as is after related:

and caused waters to run down like rivers ;
from the descent of the rock, which followed them all the way in the wilderness; this was a most marvellous thing, that water should flow from a flinty rock upon striking it, from where fire rather than water might have been expected; and that it should flow in such great abundance, and that from a rock in a wilderness.