Here in the Mayenne there is a problem with water pollution. There is enough fertiliser run-off going into the rivers and streams that the Powers That Be are worried about it. I don't strictly know if the water fails to meet EU standards, but, evidently, Something Must be Done.
There used to be many water mills along the rivers that thread through the Mayenne, and each one had its dam and sluice gate for water management. The mills have fallen into disuse but the dams and sluice gates remain, and these slow down the flow of water enough, apparently, to cause the pollutant concentrations to reach unacceptable levels. The solution being proposed (and, by degrees, inplemented) is to destroy the old dams to speed up the water flow in the rivers: the rivers will flow more swiftly, the water levels will drop, there will be less time for the pollutants to accumulate and they will be carried away faster. I believe that part of the argument for this approach is that sunlight on the pollutants causes chemical reactions that increase toxicity, and the less time the water is exposed to sunlight, the less the danger.
The problem that I have with this approach is that, in energy usage terms, it's short-sighted. Water mills are a low-tech and reliable source of mechanical energy that can be turned into useful electricity with a combination of three (relatively) low-tech and easily-available electrical components: an alternator, a battery and an inverter. Given the way that electricity is becoming more and more expensive, and in greater and greater demand, I'd be looking for ways to exploit reliable water power rather than to destroy ways of making it.
The moulin du Gô just down the road, I am told, would generate about 7 kilowatts. If it were my mill, that's what I'd be doing with it. I reckon that with good energy management, you could run a reasonable-sized flat in a building like that with no need for a connection to mains electricity at all.
Heating the place in Winter would be the biggest concern. 7 kilowatts (peak) is not enough to heat and cook with, using traditional methods, even if the building's thermal insulation were of the best. You could use a heat pump that would give you about a three-times return on the electrical energy you put in, but the problem with heat pumps is that they are less efficient in cold weather, and the last thing you need is a heating system that, as an innate characteristic, doesn't work well when it gets really cold.
So I'd go for burning wood as a source of heat. It's renewable and carbon neutral (over the life of the tree) and also extremely low tech. If all else fails, you can probaly still light a fire, and if necessary cook on it. That leaves the electricity to do the lighting and, usually, the cooking. With 7 kilowatts you would have to be careful about having the oven, microwave, kettle and hob running at the same time (of these the hob would consume the most), but with a bit of forethought you could prepare any given meal. And perhaps with some electricity stored in batteries, you could exceed this consumption at peak times.
And as for burning wood, the gîte here, and the house (and the pool) are all warmed tht way. You can get raw wood in the form of a felled tree, for 16 euros the cubic metre - you have to cut it up, transport it and dry it out yourself. 5 cubic metres will warm our house for the Winter (we needed less than that this year since it has been mild). My pal Leo has found a local source of oak, and yesterday we were chopping up a tree into manageable bits. A nice way to spend a sunny morning, and (give or take the petrol-powered chain saws) low tech and carbon neutral.
I've been keeping an eye open for water mills for sale. Ideally it would have to have a functional wheel, but with buildings in need of a full renovation so that you could insulate them effectively without trashing too much functional finishing. I'd have to sell this place first though, and that's a possible long-term, rather than an immediate, plan. Here's an example mill for sale. It has possibilities, but I think they're asking a bit much.