If we're doing water analogies, volts is the change in height (so, pressure) and current is the mass of water per second. Gravitational potential energy/power is therefore a direct analogy for electrical energy/power. Cross-sectional area of the channel is resistance. And if you think about it too much beyond that, you end up needing water-wheel-controlled sluice gates and water that flows uphill in special kinds of pipes, and it's probably best to stop plumbing and start thinking in terms of mathematical lego-blocks...
So yeah, you need a wall-wart with the right dam height (too much and the pipes will break, too little and there won't be enough pressure to turn the turbine), and a wide enough intake that the turbine gets its rated flow of water when the inlet valve is wide open. Note that when everything's working properly it's the inlet valve which determines the flow at a given moment, which is controlled by a guy with a clipboard and hard hat in the turbine control room, not the dam or the upstream water supply.