That's not quite the full story though, because it ignores investment made by the water companies. That is around quarter of a trillion pounds since they were privatised.
That certainly looks as if it hasn't been enough investment, but it is an investment in infrastructure at twice the rate that the Treasury was allowing the then state owned water companies to invest before privatisation. So while they do now have around £60 billion of debt, the other £200odd billion of investment has been funded by shareholders, who have received 'only' £80 billion in dividends.
The question is whether under public ownership (a) would the water companies have made £200odd billion pounds of profit and (b) whether the Treasury would have allowed £250 billion pounds to be invested in infrastructure, or whether, as for all nationalized companies, it would have been syphoned off to fund political gimmicks and pet projects for short term gain.
If you recall, every industry that was privatised had been starved of investment for decades - water, power, communications, transport. Privatisation was the only way out, because there was no more money, and British (and may other) governments can't run businesses. The problem is much more deep seated than private / public ownership unfortunately.