If you're still up,
Kipster,
1. The stuff that makes water hard or soft is calcium carbonate and magnesium carbonate. (The BBC did a great series of on-line exam revision pages a few years ago - you can still access the one on water here:
http://www.bbc.co.uk/schools/gcsebitesi ... evision/1/
As you can see from that crib, some of the UK has water with a calcium carbonate level of 100 mg/l
or below, but in most of the country, the tap water is at 100-200 mg/l
or above.
The level of calcium cabonate equivalent in Sainsbury's Still Scottish Mountain Water is 60 mg/l. In other words, it is right there in the middle of the soft water range.
It is certainly softer than most English tap water - and that's why I recommend it.
As I said before, I use it and I do get a build up in my tank. But (a) it is minor, and (b) it takes quite a while to build up to where I can even see it.
And said water is cheap. And when you make tea with it, the result is fabulous.
2. The thing about smells - there are two things that are variable with smells. One is the 'threshold' for noticing smells is personal. That is, it varies from person to person, and also from hour to hour.
It also varies with mood or what's sometimes called 'state'. As Eric Berne said, when people are what he called 'out-of-script', their sense of smell improves dramatically.
The second thing is that how many smell molecules cling to a surface varies with the material in a container. With the plastic used in my Philips Respironics plastic tank, there is very little cling. I don't have any experience with ResMed equipment.
The reason I suggested Sainsbury's distilled malt vinegar is that it seems to leave fewer smell molecules. Especially if the tank is left near an open window to dry and air properly.
3. If vinegar is no good for you and lemon juice costly, you could try Boric acid. It comes in crystals which you dissolve in water to make the usable solution. And you can order it from Boots the chemist.
4.
Pugsy - when you say, "I don't know what constitutes 'mineral water' in the UK" you are right on the money.
I could write a
New Yorker long-lead piece on the subject, but the short version is this: there is a jumble of regulations in the UK on bottled water - two different government agencies, different rules for Wales and Northern Ireland vs rules for England and Scotland. And then Scots want to go their own way anyway ...
.. Not to mention the EU contribution on the subject (and we're still subject to EU rules).
There are rules about what is 'Natural Mineral Water' vs 'Spring Water' vs 'Table Water' vs 'Flavoured Water' and 'Functional Water'.
By law, the term 'Natural Mineral Water' covers
both the stuff that's got much fewer minerals than tap water
and the stuff that's got a lot more minerals than tap water - including the kind which - as you suggest - has extra minerals
added to it.
Faced with that mess, the supermarkets just labelled that whole section of the store 'mineral water'.
So
Kipster was being accurate to local custom when she called it 'mineral water' - but there is no reason why her words automatically mean already-got-more-minerals-than-tap 'mineral water' or extra-minerals-have-been-added 'mineral water'.
And indeed, given the shelvage that I see in my local stores, the fewer-minerals-than-tap-water 'mineral water' out-sells all the other kinds.
At least it does where I live.
If I can say again what I've said before. Medical quality distilled water is really expensive here. It costs an arm and a leg. The next best thing -
in terms of time and money and quality and no fuss - is the very low-level of minerals - repeat very low-level of minerals - bottled water from Scotland.