I know that Francis turbines need *hydraulic head* and that Kaplan turbines depend on the *flow* of water, but I mean, what turns them? Is it merely the impact of the water hitting them, or the act of water flowing through? I ask this because I was wondering if it would be possible to create a hydroelectrical system using a (hypothetical) really, really, dense fluid instead of water.

Wikipedia says:

"The power available from falling water can be calculated from the flow rate and density of water, the height of fall, and the local acceleration due to gravity. In SI units, the power is:

*P = npQgh*

where

P is power in watts

η is the dimensionless efficiency of the turbine

ρ is the density of water in kilograms per cubic metre

Q is the flow in cubic metres per second

g is the acceleration due to gravity

h is the height difference between inlet and outlet."

That makes me wonder, if there was a **lot** of density in a fluid and *no flow *at all, would a hydroelectric system work like it usually does? (Or, would it work at all?)