Many people are visiting their doctors when all they need is a drink of water.

A survey of British GPs found that about one in five consultations involved patients whose main complaint was fatigue - which is often caused by not drinking enough fluid.

While official guidelines suggest adults should drink between 1.6 and two litres of water a day, just four per cent of the 300 GPs questioned said they believed their patients were aware of how to hydrate properly.

Research suggests that many people drink just one glass of water - or even less - each day.

While many patients complain they are unable to get an appointment to see their GP, doctors say their time is being taken up by a problem that's easily resolved.

Dr Roger Henderson say he sees many patients who complain they feel tired all the time.

"There are, of course, several reasons that could be causing this but a surprisingly common cause is that they are dehydrated.

"Many of my patients do not drink enough fluid each day and only believe they are dehydrated when they start to feel thirsty," he said.

Other symptoms of dehydration appear before thirst, including fatigue, headaches and poor concentration.

He says when people start to drink more water they're often surprised at how much better they feel, both physically and mentally.

"It is, therefore, vital that drinking enough water becomes part of our daily routine."