If you winnow out the chaff in the story it comes down to rainfall in southeast England is expected to become more seasonal with less rain in the summer months, lower summer water flows in the rivers, and more frequent droughts. If nothing is done then existing water infrastructure won't be enough to guaranty water supply under worst case weather conditions.Isn't there a GBFO river running through London?
Maybe folk should stop wasting water with 15 minute showers?
So the obvious answer is to spend money on improving water infrastructure in southeast England to handle the situation. Whether that sort of answer appeals to shareholders is another question.
Not mentioned in the story is that the prairies in Canada are facing a similar problem, but in their case caused by the glaciers in the Rocky Mountains melting. Currently a lot of the summer water flow in the rivers comes from glacial melt that is replaced by snow in the winter. The glaciers however are melting faster than they are being topped up by snow so that summer river flow will start to decline over the course of this century.
The problems of London can and will be solved provided people don't stick their heads in the sand over the issue of how to find the money to build new water infrastructure as opposed to just managing what is already there.
The London story though is just a journalistic "hook" to hang the main focus of story on, which is really about cities in the third world which face the double problem of rapid population growth and decline of existing water supplies.
Most of those urban water supply problems in the third world are also solvable with the application of good management of existing resources and good planning of new supplies. You may see a slight problem with that however ...