House looks amazing especially for the price, but the driveway is just the spur from the reservoir maintenance access right next to it, so there are privacy issues. And if you have a leak or damp coming down from the ceiling, good luck. I also wonder whether there are restrictions on how the land can be used, particularly near the reservoir.
This kind of property always looks awesome, but I reckon you need to be a tradesman to be able to maintain one. Hence the price. It's a bit like seeking a £700k Scottish castle and thinking yeah maybe... And being bankrupt by actually living in it.
There is a converted engine house near here that was on Grand Designs about a decade ago. I think it eventually went for about £500k even though it has about 5 acres and is all bespoke inside, having been on for £750k initially. When I cycle past now it is covered in scaffold again.