Note that water turbine power values/size/mechanics will be rebalanced in the next update.

I really really like the idea, since rivers definately should mean water power. The only issue I have with the mod so far is, that in its current state it is just extremely superior to all other power sources, which all have drawbacks of some sort.
Fuel generaters need ... well Fuel.
Solar only works half of of the time, has reeeeelatively low output and is affected by eclipse event.
Wind power is extremely erratic in the overall output, wastes a lot of space that you cannot use for all possible things.
geothermal has a relatively high output, but can only be built at very few randomly placed locations on the map and is also behind jet another research wall.
In their current state, waterpower is high output, cheap buildings and no drawbacks but even a bonus when there is bad weather, also rivers are almost always rather accessible on most maps.

My suggestion to make waterpower mechanically distinct and not overpowered would consist out of 2 changes:
Reduce the base output a lot (since they are small and cheap buildings) and/or increase their size/cost so you cannot spam them in every river.
Take some of the fixed power output away emphasize on the "bad weather bonus" more somewhat like wind power. But since it takes a while until all that rain gets into a river, make the output rise slowly but steady while there is rain (and maybe a short time after the rain) and let it slowly drop when it is dry. This way your water power would have a nice way to be utilized between Solar and Wind

Thank you very much on your balancing suggestions, our next patch will be modifying power output so that the turbines aren't so "consistent", and we've fixed a bug that surprisingly hasn't been reported regarding the terrain under the turbine and made it so it will only produce power if all 4 tiles under the turbine are DeepMovingWater. As for rain benefit and base output, we still need to take a look although we've considered having the maximum potential power produced being less than that of a solar plant.

As a matter of fact, I probably just missed that bug since it hasn't occured to me to place a water turbine anywhere without water ;) I appreciate it a lot that you're going the "less consistent power approach.

I agree on the power output being too high. I counted that I could put 20 of them next to each other next to the base and that is just a ridiculous amount of power. The river can hold three times more.
The size of the generators is fine, but I suggest a proximity check so that you can't place them too close to each other. That would reduce the ability to spam them.

I have a concern from the A17 version turbines being considered cover. I developped a whole river and dam for a megaproject castle-base, but raiders often entrenched themselves in the water behind turbines since they had an 80% cover bonus. The resulting shootout between my stone ramparts, towers and turrets actually favoured raiders because of how effective hiding behind a turbine was. I would suggest eliminating the cover bonus entirely, since an underwater turbine would probably suck in anyone swimming behind it for cover ;). Great mod by the way! Also I agree that they generate power far too reliably - I deliberately staggered their spacing to prevent abuse and for a better aesthetic look.

Interesting, did not realize the cover effect and that raiders would hide using them. I'll look into it, thanks for the suggestion.