peebee
Out of Control
I liked that map, but then I am a sucker for colourful cartography. One I dug out on an earlier discussion (Jan 2020, but a different forum) was:See the attached PDF for a view of what I'm talking about. Where it rains a lot, the water is typically soft. The scenery is often nicer in those places too.
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Only England and Wales, but a bit more detailed and doesn't suggest my water is harder than somewhere else that I know has harder water. But neither suggest whether they depict "Permanent Hardness" ("true" hardness, due to Calcium and Magnesium salts mainly) or "Temporary Hardness" (Carbonate Hardness, or Bicarbonate mainly), but in the UK they go roughly hand-in-hand. "Alkalinity" has more in common with "Temporary Hardness". The scale on the first map is in "as Calcium Carbonate" but that doesn't mean is Calcium Carbonate of which there will be virtually none in UK water (its a convenient, and arcane, unit label).
Even more colourful and perplexing is maps of the underlying geology like >here<. Now that's Pretty (capital "P"!). Thanks to Eric (different forum) for digging me that one out. Still relevant, you can make estimates of likely water compositions from it, including surface water compositions (leached from "superficial deposits" - I had never guessed they went to such detail! You can turn "superficial deposits" off if they induce headaches!).