At the time I was there I was really obsessed with the effects of water in distilled spirits (not that I'm over it), so I followed up with some super specific questions about the pH and TDS of the water sources. I never ended up putting up a blog post about it but now it's about time.
Note that the Highland and Islay distilleries have slightly basic water (above 7.0), while the Island of Mull distillery water is slightly acidic. It would be more typical for Islay water to be acidic, as it typically runs through decaying vegetation through peat bogs, but at Bunnahabhain they collect the water upstream, two miles from the distillery. (Read more here.)
Deanston (Scottish Highlands slightly north of Glasgow)
Water Source: River Teith
Total Hardness ( mg CaCO3/ L ) 19.5
Colour (mg/L Pt/Co scale ) 20
Calcium ( mg/L ) 6.18
Water source: Margadale underground river
Total Hardness 120.7
Tobermory (Isle of Mull)
Water Source: Gearr Abhainn
Total Hardness 21.4
To see how these water sources compare against typical Highland/Islay water, see this post as well as the whole Water Project series here to see how different water sources change the flavor of whisky before and after distillation.