Tesco and Asda have both been forced to deny rumours that they are selling tap water for 17p a bottle.
The Daily Mail recently reported that both supermarkets' own brands of still water were nothing more than a filtered down version of mains water - but spokespeople from both supermarkets have claimed that branding the product 'tap water' was inaccurate.
Speaking to mirror.co.uk, an Asda spokesperson said: "Our Smart Price water is treated to remove chlorine, further filtered then bottled. If sparkling, carbon dioxide is added for a bit of fizz. The label on the bottle tells our customers just that."
Tesco released a similar statement. However, both supermarkets have been urged to update the labels on their bottled water so that it is more clear how the product is made.
Jacob Tomkins, who is director of UK water quality company Waterwise, has accused Tesco and Asda of misleading customers with their current labelling.
He told thisismoney.co.uk: "They are taking tap water that is perfectly good to drink and has already been filtered and checked many times. They are then filtering it again for no good reason, sticking it in a plastic bottle, transporting it hundreds of miles across the country and leaving it on shelves to get hot and cold for weeks on end."