Manx Utilities says a contamination incident involving water supplies in Lower Douglas last week involved the Ben my Chree.
Sea water was accidentally pumped into the fresh water supply as workers washed down the Steam Packet vessel during a routine procedure.
Steam Packet Chief Executive Mark Woodward says connecting to the fresh water supply has never caused problems before - but a backup pump kicked in, forcing harbour water into the system.
Manx Utilities technicians have fitted a non-return valve to the system to make sure such an incident can't happen again.
Commissioners looking for new clerk
Nobody charged for paper Manx Utilities bills, says chair
Should cohabiting couples get married tax breaks?
Repairs on Peel Power Station to get underway
Manx Care doctor survey to be discussed by Tynwald
Weather warning for snow tonight
MHK queries safety at primary school in Ballabeg
Gales put two ferry sailings at risk tonight