We would love to be able to give out water to everyone who wants it, but we can only do the best we can with the stocks we have.

London Underground spokeswoman

A Tube spokeswoman said the Met Office would be advising them which days will qualify.

She said: "The water is being handed out at the barriers of the two stations during the morning rush hour.

"As expected it was a sell-out on the first day, people were very receptive to the idea.

"We will decide on when the other seven days will be, when the Met Office tell us it will be a hot day."

Perfumed platforms

The spokeswoman denied that the scheme was a publicity stunt to revitalise the image of London's beleaguered tube network.

London Underground deny the scheme is a gimmick

"We would love to be able to give out water to everyone who wants it, but we can only do the best we can with the stocks we have," she added.

"This is not a cheap way of getting good publicity. This is a trial and we are doing it in order to look at different ways of making journeys on the tube a little more comfortable."

The spokeswoman admitted the Underground is "cash-strapped" and that until there is regular new investment, health and safety issues would take priority .

Earlier this year perfumed platforms were introduced to bring a sweeter smell to tube stations.

The scented platforms were suspended for a month at two of the stations earlier this year because of claims of allergic reactions to the perfume - a Health and Safety Executive investigation has subsequently given it the all-clear.