We can joke (or not joke) about the Welsh story as much as we like, but there are two serious issues here. First, we've been several times round the Wrekin when it comes to a national water grid, and I've no doubt it will all be forgotten when the heavens open in the SE, as they surely will - only to be resurrected again in another 40 years' time, or whenever. Second, devolution/independence will throw up so many questions about who pays for what that I suspect that everyone, for and agin, will wish they'd never gone there in the first place.
Surface water drainage is an important factor - many people pay for surface drainage when it isn't drained at all. Many people have soak away's or drives that don't drain to the main sewer. If they go onto a water meter, all these costs are taken off the bill and you end up paying very little.
People are paying default payments when they don't need to.