The common advice to drink eight glasses of water a day doesn't hold water, say nutrition and kidney specialists who want to dispel the myth.
"What drove us to drink two litres of water a day?" asks an editorial in this week's issue of the Australian and New Zealand Journal of Public Health.
The recommendation was driven by vested interests rather than health, suggests author Speros Tsindos of the department of dietetics and human nutrition at La Trobe University in Victoria, Australia.
"Humans need to maintain fluid balance and need to drink water when required, but should also consider fluid in unprocessed fruits and vegetables and juices. There is further evidence that water and a well-balanced diet does far more than water alone," Tsindos wrote.
"Water is important for health; however, the recommendation of eight glasses of pure water per day appears an overestimation of requirements."
Even a baked potato is 75 per cent water, said nutrition Prof. Susan Barr of the University of British Columbia, who sat on a Canadian-U.S. committee that looked at fluid intake.
"There's nothing magical about water from a glass of water as opposed to water from a food or any other beverage," Barr said.
Drinking caffeinated beverages such as tea and coffee do not lead to dehydration, said Dr. Stanley Goldfarb, a nephrologist at the University of Pennsylvania who reviewed research claims on drinking eight glasses of water and studied how the kidneys handle it.
Let thirst guide you
"Drinking the coffee will count towards your total water intake for the day," Goldfarb said.
Goldfarb said despite the common idea that it's important to "drink eight glasses of eight ounces of water" a day, "There’s no evidence that benefits health in any real way and it really represents an urban myth."
There's no evidence you need to drink more water than what thirst dictates, Goldfarb added.
Studies on desert nomads showed people can consume minimal amounts of water in harsh environments. The military has also looked at how much water soldiers need to take with them when patrolling in hot climates without harming their performance.
"If one is just playing a game of tennis in an indoor facility, for example, or having a short run on a treadmill in an air-conditioned gym, the need to maintain hydration during that is just non-existent," Goldfarb advised.
People have died of dehydration and from drinking too much water too quickly.
A good guide to tell if the body’s finely tuned fluid balance is to check the colour of your urine. If it's very dark, you're on the dry side; if it's very light or translucent, then you need to drink a bit less water, said Dr. David Price, head of family medicine at McMaster University in Hamilton, Ont.