Conforming to the 2012 energy regulations


Does anybody have any advise on installing hot water systems that conform to the new 2012 regulations. We are just about to ask for a permit de contruire for an existing barn that will eventually be converted into 6 apartments (2 per year). And have just been told we must also conform to the 2012 laws. We have decided to go with the inverter system for our heating but are stuck on hot water. Each apartment will need its own separate hot water supply. As always the budget is tight and looking at the price of the thermodynamic boilers I got a bit of a shock. I know in the long run, they are super efficient and save on fuel bills etc but that doesn't help us initially, it is key that the installation cost is as low as possible. Any advise would be greatly appreciated.