There was a time when children quenched their thirst with free, flowing water from school drinking fountains. But many now constitute a health risk, so the Assembly government wants schools to replace them with expensive coolers or bottled water.
But it appears thousands of pupils might be going thirsty because schools have not followed official guidelines. Some pupils could still be using fountains dating back to the beginning of the last century.
Two years ago the Appetite for Life plan proposed that all schools should ensure every child had access to free, preferably chilled, water at different places around the school, away from the toilets.
Health experts suggest schoolchildren need to drink at least three to four glasses of water per day, more when exercising or in warm weather.
A study in 2004 at 384 schools in poor areas of Wales showed pupils' concentration and behaviour improved if they could drink more water. So water coolers were given the official seal of approval.
But 600 schools in Wales, about one in three, are still without them. It would cost pound;400,000 to provide them, but the Assembly government says it is up to local authorities to apply for funding.
Appetite for Life recommended schools should have taps in classrooms, water coolers so that pupils could fill bottles, or covered jugs or urns in school canteens.
The Assembly government spent pound;225,000 on mains-fed water coolers and personal water bottles for the 384 schools that took part in the 2004 study. And in 2007, 900 schools within the Welsh Network of Health School Schemes used Food and Fitness grants to buy water coolers.
But anecdotal evidence suggests many schools are relying on out-dated water fountains, often in unsuitable places such as toilets.
In July, former pupils from a secondary school in a deprived community gave evidence to the Assembly's children and young people's committee investigating child poverty. The only free water, they said, came from several dilapidated drinking fountains, half of which were broken or dispensed warm water. There was no free water in the canteen.
Nickie Brander, campaigns organiser for Eric (Education and Resources for Improving Childhood Continence) said that although Wales is doing better than England, it lags behind Scotland, where almost every school has water coolers.
"(Wales) has come a long way but it needs to go further to ensure all children have the same chance," said Ms Brander. "Very few schools, unless they are forced to, are going to put in water coolers."
An Assembly government spokeswoman said Pounds 4.7m had been made available over two years via a specific grant scheme across all authorities.