Bottled water is to be banned from government offices amid increasing concerns about its environmental impact.
Cabinet secretary Sir Gus O'Donnell has written to the head of every government department ordering them to phase out bottled water.
It is hoped that only tap water will be available in government meetings by the summer.
Sir Gus wrote: "The government is committed to sustainable operations across its estate and I have made this issue one of my key priorities for the civil service.
"Today's announcement is a small part of a much bigger programme of action in this area."
Some departments, including the Department for Environment, Food and Rural Affairs (Defra), Food Standards Agency and the Department for Business, Enterprise and Regulatory Reform, have already stopped offering bottled water.
Defra revealed it used 12,600 bottles in the last year before it switched to tap water.
Environmental activists argue tap water uses 300 times less energy to create and distribute than bottled water and produces much less waste.
Last month environment minister Phil Woolas joined in the criticisms of bottled water, arguing it was "daft" for Britons to consume six million litres of it when tap water is safe and cheap.
"It borders on morally being unacceptable to spend hundreds of millions of pounds on bottled water when we have pure drinking water, when at the same time one of the crises that is facing the world is the supply of water," he told the BBC Panorama programme.