A union has claimed passengers face a “summer of delays” across the London Underground network because drivers are being denied access to clean drinking water.

Train drivers’ union Aslef warned frontline staff will be forced to take unscheduled stops for water after TfL changed the contractor it uses to supply water coolers.

The union claimed as part of the changes, water coolers had been removed from tea points and locations where drivers change ends to reverse trains.

It also said drivers had been told they would have to wait until their break in future to go and get a drink due to the new measures.

Finn Brennan, Aslef’s organiser on London Underground, said: “When your working day is spent in a metal box deep underground, cool clean drinking water isn’t a luxury, it’s a necessity.

“Transport for London rightly reminds passengers to carry water with them in hot weather, but at the same time they are taking away the facilities where drivers can get water from during their duties.

“The inevitable result will be that drivers will be forced to take additional unscheduled breaks to avoid the serious dangers of dehydration.

“This will mean that trains are stuck in platforms and additional delays for passengers right across the Underground network.

“It beggars belief that senior TfL management think it is ok to treat train drivers like this and are utterly careless of the impact on their passengers.”

Millions of Londoners have already been hit by a string of delays and cancellations this year due to union disputes with TfL.

In February, RMT members in east London also went on strike over plans to move seven members of staff from its Leytonstone and Hainault depots to other parts of the network.

The action shut down the Central line between Leytonstone and Epping.