Well it's even worse than that. This analysis conveniently misses out two vital facts, effectively making it appear to be dishonest bollocks.
What is being used as a measure here is improvement. Which would be fine if all countries of the UK started out as equally good/bad. But that is not revealed. So if the Northern Irish water supply started out much better than the English, then by this measure it can be suggested to be performing worst.
But for all we know Northern Irish water hasn't improved much because it had little need to. While the English water may have massively improved itself from bloody awful to just mediocre. That doesn't mean that privatisation has done wonders for England that Northern Ireland missed out on.
We also are not told just how much England is paying per head for their water, compared to Northern Ireland. If the English are paying through the nose in comparison, then of course they'd expect to be seeing greater improvements. And we also aren't shown that the money that is getting charged is being handled efficiently and they're getting their money's worth. For all we know, England could be getting massively ripped off by the private water companies and not getting what they're paying for.
But then including these figures maybe wouldn't prove how wonderful privatisation has been for England. So best swept under the carpet.