Can you imagine spending every day at work with a hangover? That is the nearest adults will come to the feelings of dehydration experienced by children who have little access to water during the school day, according to a teacher interviewed by Sean Coughlan of BBC News Online.
Hilary Reed, a teacher with the Brighton and Hove learning support service, says that dehydration is contributing to academic underachievement and poor behavior.
And a project in Brighton, England, is examining whether a bottle of water could be schools' secret weapon in improving test results.
"Day after day, I come across tired, lethargic and irritable children, unable to concentrate – often due to dehydration," she says.
"I also witness a succession of children going into the school sick-room with stomach aches and headaches, mostly all 'curable' with a drink of water."
And putting this theory to the test is a project in Brighton in which pupils are being allowed free access to water throughout the day – and are encouraged to drink more water at home.
This School Water Policy is in place in two-thirds of the local authority's primary schools and it is also to be implemented in a secondary school.
Later this month, research will begin to see whether this has any beneficial impact on behavior and performance.
Pupils have their own water bottles on their desks at school, from which they can drink whenever they want.
Most provide their own bottled water, or sports bottles which can be topped up from the tap. But sponsors are also providing free bottles, so that all pupils can participate.
The intention is to make sure that children get nearer to the 1.5 litres of water needed every day by five year olds and the 1.75 litres needed by 10 year olds.
Without this water, Reed says that there is a pattern of lethargy, temper tantrums and illness.
And after a couple weeks of increasing water intake, she says that there are visible improvements, such as greater alertness, particularly in the afternoon.
"I've seen the benefits," says Debbie Crossingham, head teacher of Westdene Primary School in Brighton, which is taking part in the project.
In her teaching career, she says she has seen how dehydration can contribute to headaches and other sickness problems.
"I'm sure that increasing access to water can also help in improving results, along with other factors."
Drinking water at times such as after the lunchtime break can help pupils cool down and calm down, she says.
And an awareness of the need for water can also help teachers avoid headaches (adults should be drinking two litres of water per day).
Pupils at Westdene Primary School seemed ready to accept this water-friendly approach, swigging away at their bottles and saying that it was much healthier than the carbonated drinks aimed at their age group.
Although they were also clearly aware of the advertising and strong images associated with "fizzy" drinks.
Reed, who has been teaching for 28 years, says that she has seen a two-fold problem emerging with a lack of water.
Crossingham says there are observable benefits to giving more water.
The amount of water available to pupils has diminished – with many water fountains in schools around the country not working or inadequate for the numbers of pupils.
This means that pupils can spend the entire school day without any water.
And she says that filling this thirst gap has been the rise in carbonated drinks, which bring other problems for health and behavior.
At home, she says that many more younger children are using "adult" drinks such as tea and coffee, which in terms of rehydration are not as effective as water.
As many as one-fifth of pupils drink no plain water at all, she says, which in the long term could have serious consequences for health.
The School Water Policy is a "humanitarian issue," she says, which at relatively little expense could have a positive impact on schools.
"When you see Tony Blair speaking on a platform, he always has a bottle of water beside him. Why can't children have the same? It is outrageous that they do not have access to water."
And she highlights that this low-tech, simple scheme is far less difficult and expensive to implement than the introduction of information technology. "It is so basic, such common sense."
"It has been possible to put a computer into every classroom, but not a bottle of water," she says.
She also says that there has been a failure from the Department for Education and Skills to promote the importance of access to water.
Pressure on budgets means that schools might not prioritise the repair or installation of water fountains.
And Reed argues that there should be an obligation to provide such facilities and a separate budget available to cover the cost.
In response, the Department for Education says that its "Healthy Schools Guidance is aimed at encouraging schools to be safe, secure and healthy environments... Rather than being too prescriptive, the guidance empowers schools to make decisions which are right for them."
And it says that its guidance to school caterers "contains the Secretary of State's strong recommendation that drinking water should be available to all pupils every day, free of charge".
There have been previous experiments which suggest that hydrating the brain really does improve results.
Pupils at Corstorphine School in Edinburgh, who were drinking water throughout the primary school day, saw improvements in test results.
And in Yorkshire a water in schools project has followed the success of a pilot scheme in Leeds.
Source: BBC News