New Zealand recommendations suggest an adequate daily fluid intake is about 2.2 litres for women and 3 litres for men.
However, this includes fluid found in food and beverages.
La Trobe University lecturer Spero Tsindos said people could get their daily fluid intake from fruit, vegetables, juices and even tea and coffee.
“If you’re feeling thirsty then drink by all means a beverage. It doesn’t have to be water,” Tsindos said.
“I’m not saying you shouldn’t drink water. I’m saying the need to drink two litres of water on a regular basis is a complete myth.
“We should be telling people that beverages like tea and coffee contribute to a person’s fluid needs and, despite their caffeine content, do not lead to dehydration.”
He said drinking a large quantity of water in one sitting to reach the daily intake level was pointless because it would not be distributed where it was needed. It would just dilute the urine, he said.
Drinking large amounts of water to lose weight would not work either without a low-calorie diet, he added.
“There is further evidence that water and a well-balanced diet does far more than water alone,” Tsindos wrote in The Australian and New Zealand Journal of Public Health, published this week.
“Water is important for health, however, the recommendation of eight glasses of pure water a day appears an overestimation of requirements,” he said.
The eight glasses a day notion may have stemmed from guidelines published in the US in 1945, Mr Tsindos wrote.