... is that the growth in sales of bottled water is a bad thing, and shows the ultimate decadence of our society.
It's not that simple, of course - it rarely is.
I drink bottled water at work, now. We are provided with half-litre bottles as required - as much as we can reasonably drink - in addition to tea and coffee. It didn't happen when I started in the job, though we did used to be able to get soft drinks free - orange juice, lemonade, cola. So I now drink bottled water at work instead of soft drinks. I would not be able to take my own tap water into work. Well, not unless it was in a container of less than 100ml. Water is much better for my teeth, and probably cheaper for my employer!
I used to work for an airline which on longhaul flights would provide all passengers with a bottle of water. So the passengers would drink bottled water in preference to more soft drinks and alcohol.
You also see a lot of what I suppose I now ought to call the "younger generation" not drinking tea or coffee, but carrying bottled water around. In restaurants, even fast food places, and at places like Boots where you can get a packed lunch for less than a fiver, bottles of water are one of the options.
So in a lot of cases, it isn't so much the case that people are drinking bottled water instead of tap water. Yes, they could wash up and rebottle their own tap water in some circumstances, it's true, which would be better. However, the fact is that a large proportion of the use of bottled water isn't at the expense of tap water. It's at the expense of soft drinks and beverages which are less healthy than water.