A study into Tonga's tax on sugar-sweetened drinks has found it may have led to an increase in bottled water production.
The research, by a team from Otago University, is one of the first studies of such taxes in the Pacific, where 14 countries and territories have introduced them.
Since introducing its tax in 2013, the Tongan Government has taken about $US3.4 million (approx $NZ5.1m) a year in revenue.
The tax has been raised twice since it was first introduced, and now sits at about 31 percent, which led to about a 17 percent increase in the price of a particular brand of soft drink, according to the research.
One of the researchers, Professor Nick Wilson, said it did appear to have had the desired effect of increasing prices.
"And that led to a reduction in imports of the beverages and it actually resulted in an increase in locally bottled water," he said, adding it showed people were choosing not to buy sugar sweetened beverages.
"So all these things are potentially good for public health."
However Wilson said more research was needed into whether a tax had any effect on rates of non-communicable disease in Tonga, where obesity, diabetes and other chronic conditions were an acute issue.
"We were able to adjust for some of the key factors, but some of these things do need further investigation. It's quite complex to deal with."
Still, he said it was a research first for the Pacific, and showed promising signs of efficacy.
"When you combine this evidence from Tonga and the international evidence that sugary drink taxes work, governments should be applying them."
"I think we know enough for governments to act but obviously further research will help refine these taxes and work out what is the best level to set them at."