At first I thought perhaps you could use tsunami wave speed data for a very rough estimate. But that's wrong, because tsunami speed (roughly between 500 and 900 km/hr depending on ocean depth) is a measure of the wave energy propagating through the ocean, not a measure of the water's speed over ground.
Instead, perhaps one could start by using a model for the flow of water from a catastrophic dam breach. Hopefully someone more mathematically inclined than I will give it a go...
One spring day the rotting ice broke, the lakes surged free, travelled downhill as they must, ending in the gulf of mexico.
Took all summer, carved the Mississippi valley. According to the storey in the interpretive center near Pike's Peak.
(Rockets going into orbit aren't just climbing, they're also building ground-speed. If there were an imaginary tower from ground to low-earth-orbit height, climbing it wouldn't put you in orbit - if you let go of something at the top of that tower, it would just fall.)
You do get some relative velocity due to the earth's rotation, it's just not enough to put you in orbit until you reach geosynchronous altitude (from your imaginary tower, not necessarily the imaginary sphere of water).