AUCKLAND, May 16 - Decile-1 Yendarra School in Otara has only allowed students to drink water and milk since 2007 and there's been a significant improvement in students' teeth since, the Dental Association says.

Ten years of data shows the average number of cavities per student has dropped while the number of teeth being pulled has nearly halved, spokesman Rob Beaglehole says .

While there was no silver bullet for combating sugary-drink-related harm to teeth, the association was now encouraging schools and early learning services to go "water only", he said.

"A broad approach is needed, including bringing the education sector with us. It really is that important as a health issue."

The association has been pushing for schools to drop sugary drinks since June with Riverlands School in Blenheim recently adopting a water-only rule as well.

"We hope more schools will come on-board, as it is an effective way to make healthy change within our schools," chief executive David Crum said.

Tooth decay is listed among the most common reasons for children's admission to hospital in New Zealand.