More than 100 workers have been airlifted from a North Sea oil platform after diesel was found in the fresh water system.
The contamination was discovered on Taqa Bratani’s North Cormorant installation on Sunday.
Employees remained on the rig overnight and were provided with bottled water as the company isolated the source of the substance and tried to flush it out.
It emerged yesterday that more extensive cleaning was needed and the 134 non-essential members of staff were transported off the platform on about 10 helicopter flights.
The 54-strong essential workforce, who stayed behind to keep operations going, are being supplied with fresh water and microwave meals to limit washing up.
A Taqa spokesman stressed there had been no emergency evacuation and said no-one had consumed any of the contaminated water. The platform also remains operational.
Aberdeen Coastguard was notified about the incident as a precaution, but was not involved.
The spokesman added: “Further cleaning is taking place to ensure no diesel remains on the walls of the water pipeline or the tank.
“The welfare of the people on board the installation is our main priority.
“As the installation currently has no running water, a downman of those people who were not required for the continued safe operation of the installation or the cleaning operation has taken place.”
The majority of the workers were flown to Scatsta and Sumburgh airports in Shetland, from where they continued their homeward journey, while 17 were transferred to the nearby Eider installation.
RMT union regional organiser Jake Molloy said incidents of water contamination were not unusual but could cause “no end of grief” for those affected.
He said: “The real problem starts now in trying to clean all the systems out. That’s the real task they have got. The pipelines have to be emptied and flushed out and there will have to be a major cleaning exercise before staff can go back.
“It’s a welfare rather than a safety issue. If you can’t shower or get a drink of water, you can’t carry on working.
“There’s no significant risk to staff – it’s more about accommodating them in an environment where they have ready access to clean drinkable water and can live reasonably comfortably.”
The cause of the contamination is not yet known, but an investigation is underway. The cleaning operation is expected to last a few days.
North Cormorant, which is situated about 310 miles north-east of Aberdeen, produces about 9,000 barrels of oil per day.