One litre of water is obtained from solid foods in a good average diet.

One litre of water is obtained from solid foods in a good average diet.

How much water should we each be drinking a day? And is it healthy that we're constantly asking ourselves if our intake is adequate?

Twenty-six years ago, Australian cricketer Dean Jones was berated during an epic Test innings in India for asking to leave the scorching pitch after constantly vomiting from dehydration. His captain Allan Border barked that if he couldn't handle the conditions, ''then let's get a real Australian''. Only after Jones finished on a score of 210 was he rushed to hospital.

There's a huge market in bottled water and energy drinks and I think, as a society, we're becoming waterlogged. 

Today, no elite athlete is allowed to compete in any endurance or high-intensity sport without the chance of taking liquids either in the breaks, or on the run. Children at school even have formal ''supervised instances of water intake'' to ensure adequate hydration.

''It's sometimes quite ridiculous,'' says the sports science director of the Collingwood AFL club, David Buttifant. ''You see people sitting in their offices with massive 1.6-litre bottles of water or sports drinks and they're drinking two of those a day. There's a huge market in bottled water and energy drinks and I think, as a society, we're becoming waterlogged.''

While elite athletes competing outdoors in temperatures above 30 degrees can indeed manage two of those bottles in a couple of hours - they can lose up to 5 per cent of their bodyweight in fluids in a match - the rest of us don't need anything like that.

The Australian Institute of Sport used to publish specific guidelines for how much everyone should drink but abandoned those a few years ago because the amount depends so much on an individual's build, how intensely they're exercising and for how long, the temperature, their age, their state of health and what kind of foods they eat.

''So now we typically recommend about eight glasses of water a day, which is about two litres, but there's been no actual research done on how much we need to drink,'' says AIS senior sports dietitian Bronwyn Lundy. ''In addition, if you have plenty of fruit and vegetable in your diet, you'll get more fluids, but if you're eating highly processed foods then you'll get less.''

Top athletes have been known to lose up to three kilograms in weight during intense activity. People can weigh themselves before and after a bout of hard exercise, Lundy says. ''They should aim to immediately replace 70 per cent of that - a litre for every kilo lost - in water,'' she says.

But for the most part, we're becoming too preoccupied with fluid consumption, according to CSIRO senior research dietitian Pennie Taylor.

''We're now all just a bit fearful of not getting enough,'' she says. ''People are confused about how much to drink and what to drink and they're obsessing over it.''

Generally, she recommends women drink up to 2.1 litres (eight cups) a day, and men up to 2.6 litres (10 cups). About a litre is obtained from solid foods in a good average diet - fruit, vegetables, yoghurts and soups - although little from foods such as bread and breakfast cereals, which can have high levels of sugar, salt and fat. Liquids such as coffee, alcohol and sugary, caffeinated soft drinks can have a diuretic effect and cause or worsen dehydration.

''Intense, or endurance, exercise means you'll need more hydration, and younger children and older adults often need more because they tend to dissipate fluids more,'' Taylor says. ''Thirst should be a good guide and urine should be pale yellow, not too dark.

''And with extreme sports, that's when people need electrolytes, which some sports drinks are designed to provide as salts do leach out of our bodies.''

Our obsession with drinking enough has led, in turn, to worries we might drink too much. In 1995, 15-year-old Sydney schoolgirl Anna Wood died from water intoxication after taking an ecstasy pill. Three years ago, a 28-year-old woman collapsed and died in California after taking part in a radio contest to see who could drink the most water without going to the bathroom.

''But those are extreme cases and in normal circumstances no one's going to drink litres of water and not feel the need to go,'' Taylor says.

The best option? It's on tap

Fluid fads, such as coconut water and vitamin water, often carry many unnecessary kilojoules. ''Coconut water provides about 225 kilojoules per 250-millilitre glass, while water is zero,'' says CSIRO senior research dietitian Pennie Taylor.

''And sports drinks were originally developed to improve hydration of those participating in intense or endurance-based sports and physical activity, with high amounts of sugars, salts and citric acid. So the real miracle drink, with no kilojoules and the best fluid for hydrating the body, remains plain water.''

Despite this, a study by dieticians Dr Gina Levy and Professor Linda Tapsell of the University of Wollongong found sales of sugar-sweetened sports drinks grew by 42 per cent between 1997 and 2006. By 2010 annual growth was 20 per cent.

A study by Deborah Tate, an associate professor in health behaviour at the University of North Carolina found that by replacing caloric beverages with non-caloric drinks such as water, people were twice as likely to lose 5 per cent of their total weight in six months as those who continued drinking caloric beverages.