Pretty much anywhere you go outside of larger cities in Scotland(if you like outdoorsy stuff like I do) has warnings that tap water is supplied directly from the nearest stream/river/lake and is unsafe to drink untreated. I'm perfectly happy to drink tap water nearly anywhere in the UK but any time we go camping in Scotland bottled water is a must because safe tap water is a rarity.
I guess it's possible that such places exist that have a private water supply - but in general tap water in Scotland is perfectly safe and tastes lovely. I've certainly never seen a sign anywhere in Scotland that warns about the tap water not being safe.
This is nonsense, I grew up in Scotland and travelled widely and I’ve never seen such a notice.
Stayed up in Glencoe literally 2 months ago and these notices were everywhere. Same when we camped next to Loch Ness, Loch Lomond and in Cairngorms.
I've seen the 'private supply' notices but I've never seen them say that water should be treated first (nor have I ever had problems with not.) It's disappointing if they're starting to do this in a blanket fashion.
Not Scotland, but I've travelled a lot in Wales, and most, if not all, of the cottages we have rented have had these notices.