Water is under the control of local water companies in France and you'll need to find out who manages your supply of water or the supply of your future house. That can be done relatively easily by finding out what water companies are around in the area and then calling them to speak to them. In rural areas they may not be open every day and not all day for most of them too.
When buying a house, you'll have to have the water changed over to your name. That means you will usually have to provide the following information and proof of residence:
Identity papers (passport or Carte de séjour, for example).
A RIB, or the details of your French bank account to have the direct debit set up.
Proof of ownership fo the house (something from the notaire, if you are still in the final stages of purchase).
It's a good idea to do this all a couple of weeks before you move so that you can get all the admin finished.
You will have to pay a service or administrative charge and then you will have to provide proof of the meter (usually a photograph suffices so they don't have to come, or maybe sometimes they might just take your word on it). Then you will get a bill roughy six months later telling you how much you have consumed in terms of water. If you haven't asked for it the first year (it's not always possible that first year), then you can get yourself set up with monthly water payments that are based on your previous consumption. You will have to either go in or make a call. If you send a mail, then they will probably call you, especially in rural areas.
In rural places, you should also check the local mairie from time to time as they will post information about the quality of the water that is being supplied and if there are any problems with it. Your neighbours will probably be better informed on this, however, and they will usually see you up to date about any need to boil water or to buy bottled water. But, the mairie does usually provide bottled water to inhabitants if there are (rare) problems that occur.
Someone will just come and read the meter for your property every six months usually. It is not unheard of in rural areas to be contacted by the water company for them to come and see the installation that you have, especially in very old buildings. They will be checking on the waste water and where it goes. They will usually send a questionnaire for you to fill in regarding the number of people living in the house and the number of bathrooms, etc. In the past, it is true to say that norms where far from what they are now. It is not unlikely that in rural areas, you could just have certain waste pipes (washing machine, etc), just going out into the nearest ditch on the side of the road. That will most probably have to be changed and a connection will have to be made to the mains and the sewers. This is at the expense of the property owner.
Under article L. 1331-1 of the Code de la santé publique, the water company has every right to gain access to your property and they cannot be refused as long as an appointment is made with you.
French Admin can help you with all your needs related to opening up of an account with the water company of your area, or acting as support in the event of needing assistance regarding the installation that you have and any requests to modify that.