Restaurants and cafes should serve tap water to customers as a matter of course, according to a consumer group.
The Consumer Council for Water urged the public to request tap water if they want it when eating out.
Its calls come as Mayor of London Ken Livingstone launched a campaign to promote tap water across the capital.
He said diners should not be embarrassed about asking for tap water when eating out.
Elizabeth Carter, consultant editor of The Good Food Guide, said:’We’re seeing two trends emerging at the moment. On one hand, many eco-friendly restaurants are bringing filtered tap water straight to the table and on the other, places like Claridges are introducing water menus, with some bottles costing £50 a litre.
‘Consumers need to consider both price and air miles when making their decision. Ultimately, the main message from the Good Food Guide is: don’t be intimidated by waiting staff; speak up and order exactly as you please.’
Price of tap water
The Consumer Council for Water said tap water cost around one tenth of a penny per litre.
Dame Yve Buckland, national chair of the consumer group, said: ‘The bottled water industry spends millions investing in their brands and that’s what people are paying for when they pick up a bottle of water.
‘There is no health advantage in drinking bottled water instead of water from the tap.’
Ken Livingstone’s London On Tap campaign was launched jointly with Thames Water.
London On Tap says imported bottled water produces up to 300 times more carbon dioxide per litre than tap water.