Part of the justification for price difference between wells and municipal water also comes with guarantees from the latter about it being clean and free from contamination, and that they'll treat your waste water. How much this happens in practice… well (no pun intended), I'll leave that to news stories about Flint's flammable water and Thames Water's sewage discharges.
Heck, even in my urban bay area neighborhood, I know of 3-4 people on my block with their own wells. I think it largely has more to do with when the neighborhoods were built than anything else.
I'm not at all sure what the law says about getting on the water main in the first place, but I believe it's not lawful to be disconnected even at your request.
The rules are at the level of homes and the companies which supply them with water, of which there are a small number nationwide: https://en.wikipedia.org/wiki/United_Kingdom_water_companies
Places are not incorporated in the UK the way they are in the US, so "the village infrastructure" doesn't (so far as I know) even get well-defined, which makes it hard to make national laws that prevent it being disconnected from a wider network if that's what the suppliers want to do while supplying some particular house.
There are some cities where building codes require connection to the water grid for habitability, but this is much less common for unincorporated county land.