But, in the same speech launching the International Hotels Environment Initiative, he praised the London Hilton for putting a brick in every room's toilet cistern, thereby saving several pints of water at each flush.
To date, the initiative has 11 member corporations with more than one million rooms between them.
Their first action has been to produce an environmental manual, setting out how hotels can save energy and cut their consumption of natural resources.
Prince Charles said that tourists were demanding higher environmental standards from the travel industry, the largest in the world.
'One beach, for instance, is no longer just like another beach,' he said. 'Increasingly, potential holiday-makers today want to know much more about the range of services and facilities available. . . about exactly what's in the water that shouldn't be.'
Speaking at the Grosvenor House Hotel in Park Lane, the Prince said that the new manual had disappointingly little to say about the need for international hotels to contribute to surrounding communities, especially in developing countries.
He called for 'a fresh and conscientious approach to supporting local economies by training and employing local people, by using local suppliers and local produce and local materials. Not hugely difficult - but hugely important.'Reuse content