This would depend on numerous factors - including, which waterfall, time of year etc.
About 500,000 gallons of water
Water flowing over a cliff is called a waterfall.
It's a liquid.
over 1,000 gallons
150 000 American gallons flow over every second.
Water flowing over a cliff will form a waterfall.
The position of a waterfall can change over time due to erosion of the land surrounding it. As water flows over the edge of the waterfall, it can undercut the rock, causing it to collapse and shift the waterfall's position. Additionally, changes in the volume of water or tectonic activity can also contribute to altering the waterfall's location.
By how many gallons of water are used over a set time period.
river
More then over 1,000,000,000,000,0
over 9000 roughly...
96 cubic feet will hold a little over 718 gallons