Cathay Pacific is providing passengers with bottled water on 14 aircraft after health inspectors found the water on board did not meet standards.
An investigation is underway after samples of drinking water failed to meet recent hygiene tests.
In the meantime, the airline is urging passengers not to brush their teeth using the bathroom tap water on the affected planes and is providing bottled water on board.
It has already sterilised nine of water tanks in question and the remaining five will be washed when the aircraft are next back in Hong Kong.
The investigation, led by the Department of Health, is being conducted with Cathay Pacific, the Airport Authority and the Hong Kong Aircraft Engineering Company (Haeco), which operates the water tankers that filled the planes.
