France has a schizophrenic attitude to its water mills. On the one hand you can get grants to refurbish them; on the other, the government wants to stop you from using them. They are an important part of the heritage (patrimoine), or causes of imbalances in the natural state of things.
The situation as I understand it is as follows: if your (small; less than 150 KW) mill has been in place since before the revolution, (precise dates vary between regions) you have an absolute right to use the power of the water to your own ends whatever these may be: your rights are fondé en titre. If your mill was built after this time, but before 1919 you are likely to have written permission from the state to use, in perpetuity, the water power - your rights are fondé sur titre. After this date, you probably have permission that is limited in time, and it might or might not have expired. If you need to renew permission you might not get it, especially if your river is category 1 for pollution (i.e; the least polluted). You can find a more detailed explanation here.
And now the state is claiming that water mills, even those fondé en titre, that have fallen into disuse for 20 years (why 20, exactly?) have lost their rights to water power (which idea is being challenged in the constitutional court), while at the same time, you can often get a grant to refurbish your mill, such as might be available to the Moulin du Gô just up the road.
The problem is water pollution and its impact on the wildlife population. The discharge from farms gets into rivers, and the sunlight transforms the chemicals in the water into toxins. The dams that hold the water back for the mills slow the water flow, and give the sunlight more time to act. Also, fish cannot easily migrate past the dams, with knock-on effect for birdlife, e.g. kingfishers, etc. So the parts of the civil service responsible for freshwater fish and water quality make life difficult for you by trying to persuade you to remove the dam, and the parts that like to restore the heritage like to help you out.
We went to visit Le Grand Moulin de Ste Suzanne today. This has recently been refurbished by the state, at taxpayers' expense, as a tourist attraction. It used to be a powerful mill, driving three large millstones, powered by the river Erve. The restoration is a mix of modern and traditional. The shaft of the mill wheel used to be oak; now it is steel, mounted in a modern ball race. The mechanism is the traditional English style, that is to say, the small cogs are metal, the large ones have wooden teeth mounted in a metal frame. The small cog on the shaft that drives the millstone is moved into place using a modern, manual, hydraulic pump instead of the old method where it was pushed up with a lever.
The hydraulic pump is the little box on the right; you insert a handle into the lever at the top, and pump it up and down. There are two hydraulic lifts, one each side of the small cog, looking a little like darts welded to the base plate. The one on the right has a safety clip in place to prevent it moving accidentally.
If I read it correctly, according to a little computerised display, the mill is calculated to have a bit more than 200 watts of water power available to it. Pathetic. The reason for this weedy power level is the fact that the dam to back water up for the mill has been removed. The water getting to the mill these days is (relatively) a trickle, and the wheel even stopped turning in July when the river level dropped.
The exhibits and explanitory notices in the mill give details of the history of milling, the political contexts and evolution. For example, I didn't know that it used to be illegal to own your own personal hand-grinding stones to mill flour - you had to use the baron's mill, and pay the taxes to do so.
I had never realised either, that millstones were made up of different smaller stones held together - I thought they were carved from a single stone. Apparently the best ones were made in La Ferté-sous-Jouarre, and were exported from France to the world, including Australia, the USA, and Asia. The industry employed over 4,000 workers in the mid-19th century.