This has all been a massively successful marketing con.
Camelford was indeed a disaster, but it was caused by a tanker driver putting chemicals in the wrong place - i.e. human error. It wasn't a fault in the purification systems at all.
Chazza's example goes back to 2001
The very fact that when there is a problem with tap water it makes the news is an indication that for 99.99% of the time the water companies get it right. And it's much, much cheaper, and hardly any carbon footprint. Right now, on a Wednesday afternoon in February there will be dozens of full-sized artics delivering this stuff. The number goes through the roof when it gets warm.
There was an article in The Observer a couple of weeks ago about this. It takes nine litres of water to make a bottle that can hold one titre. That way lies madness.
Just out of interest - it's been filtered through the Alps, or it's water that's been frozen in glaciers for hundreds of thousands of years - why does it have a best before date?