Mineral water has stuff in it, spring water has none - that's the theory. Perrier had to recall millions of bottles about 10 years ago when the found the filter for benzine (yep benzine) had not been change that month (deftly avoiding how long it had not been chaged since)
Perrier before filtering is about 5 times over the EC limit for benzine. Malvern water anyone? Nothing in it whatsover - unless the sheep get too close to the wells on West Malvern Rd. Yummy.