The Tongan Ministry of Health says it is working to fix cyclone damaged water and sanitation systems as a waterborne disease outbreak becomes a possibility.
The health inspector in charge of water and sanitation, Folau Hola, says the low-lying areas of Ha'apai are in a critical situation because of rising sea levels contaminating wells.
He says the majority of rooftop collection systems were also destroyed during the cyclone.
Mr Hola says it is working hard to test well water and upgrade water collection systems.
He says while there have been no reports of illness yet, the ministry is urging people to use only bottled or boiled water.
"It's a big need to do something about it before something hits the group of Ha'apai. For the next coming months, I think there will be a very big need of water for the whole place of Ha'apai. I would like to emphasise everyone to use water as wisely as they can."
A Ministry of Health inspector, Folau Hola.