Some regions in the UK have abnormally low levels of fluoride in the water supply, because of this it gets added by the water companies in those areas to bring it up to natural levels to ensure the drinking water is as good for people as can be. In addition some areas included low levels of chlorination to kill bacteria and ensure it was safe to drink. As a result of this mineral water companies started running disinformation campaigns years ago to try and convince people the tap water was bad for them because it contained "poisons" like fluoride and chlorine, which is understandable from a business POV because not many people would buy mineral water when they already paid for a mains supply of higher quality H2O.why are people buying water, just buy containers and fill up with tap water.
It worked a treat and a scarily large amount of people fell for it, hell to this day there are still people who genuinely believe not just that fluoride in tap water is bad for you but that it's added to the whole UK supply and not just the few areas where the natural level is low (even funnier they don't even realise most mineral water has levels of fluoride too).