The drinks with the highest levels of sugar were largely Chinese in style, with sour plum, hawthorn and citron honey drinks containing the most.
The Consumer Council and the Centre for Food and Safety tested over 100 samples of non-packaged drinks served in Chinese restaurants from May to July this year.
The study found 30% of the sampled drinks contained high sugar content, with over 7.5g of sugar found in every 100ml.
Among the 11 types of drinks that were sampled, hawthorn drinks and citron honey had the highest sugar content, with an average of 10g of sugar per 100ml. Luohanguo drinks had the least, with an average of 1.2g of sugar.
"The industry needs to know the sugar in the drinks they serve affects the health of the public," the report said. "Very often, the consumers do not know sugar content can be that high in some drinks."