"I haven't seen it anywhere else," he said.
"I really applaud the intention of the document, but I think a major issue is to what extent it's going to be followed through."
But Secondary Principals Association president Mike Williams said almost all schools had already stopped selling soft drinks and energy drinks.
"You would be hard-pressed to find that stuff in secondary schools these days," he said.
"I think this is like catch-up. Maybe they have looked at their figures and seen that they are not selling much to schools anyway, so they decided they might as well get some credit for it."
NZ Principals Federation president Whetu Cormick, representing primary and intermediate schools, said most primary schools did not have tuck shops anyway, and most of those that did had already adopted water-only policies.
Research led by Dr Thornley has found that a water-only policy adopted by Yendarra Primary School in Otara in 2007 reduced tooth decay in Yendarra's children by about one-sixth compared with nine other schools within 3km of the school.
The Ministry of Health has asked all food and drink industries to sign a pledge to " identify and contribute solutions that will aim to help reduce rates of obesity for all children". Coca-Cola, a leading member of the Beverage Council, has already signed.
Beverage Council president Olly Munro said the new industry pledge would still allow the sale of fruit juice and zero-sugar fizzy drinks in secondary schools.
He said the policy was less restrictive for secondary schools because senior secondary students might duck out at lunchtime to buy drinks at the nearest dairy if they were restricted to buying only water in the school tuck shop.
"Primary and intermediate school kids are not allowed out during lunchtime and morning tea, whereas at secondary schools, I think when I was at school it was from fifth form up, they are able to go out at lunchtime," he said.
He said the council, which represents the main manufacturers and distributors, could not stop schools buying anything they liked from third-party suppliers such as supermarkets.
"So we are going to work with the Ministry of Education to try and put more framework around what schools can and can't stock," he said.
"In the past the Ministry of Education has said we won't tell them what to do.
"I think when it comes to primary and intermediate, there is a real appetite to try and get as many schools as possible into water-only, so I'm hoping we will get more traction with the Ministry of Education."
The ministry's stance is due to Government policy. The former Labour Government introduced a guideline in June 2008 that schools should only sell "healthy options", but that guideline was repealed by the incoming National Government in February 2009.
Auckland University nutrition professor Boyd Swinburn disagreed that the latest initiative was world-leading.
"A lot of countries don't allow it [sugary drinks] full stop," he said.
"When you see how they do school food in Japan, it's a different universe. It's all cooked on the premises and very traditional."
What New Zealand schools sell
4% sell energy drinks
9% sell sugary fizzy drinks
12% sell sugar-free fizzy drinks
35% sell bottled water
38% sell flavoured milk
39% sell fruit juice
Source: Ministry of Health survey of schools, 2016
