The Steam Packet says it’s ’updating’ the way it works after drinking water was contaminated in Douglas last week.

The Manx Utilities Authority (MUA) warned customers not to use their tap water on Thursday afternoon, after the authority found ’an issue with the quality of water supply’.

Customers living in the polluted area, which stretched from the east side of the North Quay to the Villa Marina, were informed via social media and leaflets that were handed out by MUA staff members.

It has been established that the problem was caused by sea water being pumped back into the fresh water supply, while the Ben-my-Chree was being washed down in the harbour.

Tests are being carried out to find out what trace elements there were in the contaminated water, which had smelled of fuel.

In a joint statement, the Steam Packet and Manx Utilities confirmed that the accidental intake of sea water during the routine procedure to wash down the vessels has never occurred before, and they are working together to ensure it will never happen again.

Steam Packet 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 sea water 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 MHK 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 division 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.’

Some 700 to 800 customers were affected.

Manx Utilities worked with Robinson’s to set up bowsers outside the Sea Terminal, Tesco and Quine’s Corner.

Residents were asked not to ’drink, cook or wash with tap water’, but said that water could ’be used for flushing toilets’.

MUA said that the drinking water supply was fit to drink once again on Friday.

A number of restaurants and cafes were affected.

Noa Bakehouse used bottled water. Miles Pettit, owner of the bakery, said: ’Members of the team noticed a funny taste to the water on Thursday and got onto Manx Utilities straightaway.’