£2 billion more spend that could do more good

There are so many people in London that they want to spend £2billion more on expanding the sewerage system - note this in addition to maintenance and normal updates, this is just because of the expansion in the number of people. Oh, and recognising the problem that London has pumped out so much groundwater that ground level is in many places below sea level (hmm where did we see that before - New Orleans???)
Whereas the rest of the country still has capacity.
I can think of a far more sensible solution which would make better use of £2billion