I've set up a couple of micro-hydro systems, small scale since we don't have enough 'Fall' or 'Head' to make much power, but they put out 24/7/365 and that power adds up pretty quickly if you have flowing water.
In Central America, I saw floats made of barrels, a paddle wheel between them and the natives making power from that.
Here you couldn't block the river like that, but there aren't any laws down there,
And it didn't make much power, but it recharged vehicle batteries the folks used to light homes at night, and it recharged stuff like cell phones, ect.
Didn't get a good look at what they were using for a generator, but it would charge 4 or 5 vehicle batteries a day, so I'm guessing the output was in 12 volts and pretty good output to do that many deep cycle batteries in a day.
Falling water, I mean VERTICAL DROP, will give you MUCH more energy output because of weight/inertia when it hits the impeller at the bottom than the weight of a water wheel.
As for the 'Back Up' water generators being sold,
STAY AWAY FROM THEM!
They hook up to your water line, and the city water powers up a few hundred watts,
Usually not enough to even run the refrigerator,
And the water consumption to generate that wattage will cost you a FORTUNE when the water bill comes in!
I don't have running water on my place, so I'm screwed for micro hydro,
But if you have running water with fall, you have a gold mine as far as energy production is concerned!