"'Southern' tap water is pretty dire - very hard"

Not all of it is hard. I asked the D.J. Miles tea company (in Porlock and Minehead) whether they meant hard or soft water when they said their tea was blended to suit West Country water, and it turned out they meant water in their bit of the West Country, which is soft. But not far away in north-east Somerset the water is extremely hard. There was a rumour that this meant more than the usual number of people living to a hundred in Weston-super-Mare.
When I first lived where I am now we had lovely water sourced from underground aquifers. Some time probably in the 1980s the water suddenly changed and was no longer a pleasure to drink. So many houses had been built that the aquifers could no longer cope, and we started getting chemically treated water from the rivers. It was a nasty shock.