Investigations into the contamination of the water supply around North Quay in Douglas on Thursday have revealed it was caused by sea water being pumped back into the fresh water supply during a routine procedure to wash down the Isle of Man Steam Packet Company vessel Ben-my-Chree.

The accidental intake of sea water has never occurred before, and both the Steam Packet Company and Manx Utilities are working together to ensure that this event cannot re-occur.

Isle of Man Steam Packet Company Chief Executive Mark Woodward said: ‘When washing down Ben-my-Chree, we often connect to fresh water onshore. This has never been an issue in the past. However, on this occasion, the backup pump detected low pressure and kicked in, introducing seawater from the harbour into the system.

‘This pressurised the system on board, and as it was connected to the shore main, some seawater passed into the fresh water supply system. This would not have happened if there had been a “non-return” valve in place within the systems.

‘This was a genuine accident, which has never happened before, and it is something that the Steam Packet Company will now address. We will take steps to update our method of working.’

Manx Utilities Authority Chairman Dr Alex Allinson said: ‘I would like to take this opportunity to apologise again to all customers affected by this incident. Following the complaint from one of the restaurants on North Quay, Manx Utilities staff managed to isolate the area polluted and flush the system out, but it was initially unclear where the sea water had come from. There was close liaison with the Public Health Department and samples were sent to ensure that there had been no bacterial contamination of the freshwater system.

‘Emergency water supplies were mobilised but we had to wait until the following day to be sure that the system was clear and people were completely safe to drink the water again. The following day technicians fitted a non-return valve to the system as an extra precaution.’