I'm really skeptical of the idea that the blame for the lack of water infrastructure ought to be put at the feet of the water companies. The UK's planning system has strangled just about every infrastructure project in every domain. There is a general trend of local residents preventing infrastructure being built in the area, whether it be for water, energy, rail, or roads.

Vetocracy and nimby are ensuring the country barely shambles on until the boomers croak off. No point in putting up with construction and paying for the investments, if the current infra is juust barely good enough to last until the average voter shuffles off this mortal coil. When the older generations vote reliably and young people are apathetic, you get the current situation