Water is the wheel that keeps us going. It lubricates our joints, protects our organs, makes our blood flow and regulates our body temperature.

To replenish our body’s water, we are supposed to drink eight glasses of it a day. At least that’s the conventional wisdom, repeated to millions around the globe for decades.

Is it correct?

Doctors may continue to impress upon patients the need to drink water, but there is no scientific basis for the eight-glasses-a-day advice, according to research recently published that has exposed this and other myths.

For many, this means you can stop feeling guilty because you don’t drink as much water as you think you should.

The latest advice is: Let your thirst be your guide.

The Institute of Medicine, which advises the federal government on medical issues, said that most healthy people get the water they need from beverages and food.

The report validated research by Dr. Heinz Valtin, a kidney specialist and retired professor at Dartmouth Medical School in Hanover, N.H., who has spent more than 40 years studying water balance in the body and has written two textbooks on the topic.

‘A real urban legend’

Valtin said he recently looked into how the eight-glass dictum had become “practically … a command for good health.”

Before beginning the study, “I asked a lot of my colleagues, ‘Do you know what this is all about? Where did it start?'” Valtin said. “The answer was uniformly, ‘I think it’s a myth. I don’t know where it started, but it’s being perpetuated.'”

In 10 months of searching medical literature and talking to specialists in fluids and thirst, Valtin came up dry. He found no scientific basis for drinking eight glasses of water a day nor where the idea originated.

“It’s a real urban legend,” he said.

Valtin said his conclusion applies to healthy adults living in a temperate climate who get, at best, mild exercise such as walking. He said more water is required for people with some diseases, and in special circumstances, such as strenuous physical activity, long airplane flights and hot climates, but most people are drinking enough and possibly more than enough.

Valtin asked anyone with evidence to the contrary to contact him, but since his article appeared in the August 2002 issue of the American Journal of Physiology, “not a significant article that disagrees with my conclusion has been pointed out to me, not a single scientific article.”

But he said he had received hundreds of messages from the public, and a common theme has been: “Am I relieved! I don’t have to feel guilty anymore.”

While dismissing the eight-glass rule, the institute, which released its report Feb. 11, declined to set a number. Instead, it said the current daily water consumption seems adequate — 91 ounces for women and 125 for men daily — to avoid dehydration.

Those amounts exceed the 64 ounces specified in the eight-glasses rule, but they include all water sources, not just drinking water. The institute said 81 percent comes from drinking water and beverages and 19 percent from food, which brings up a second myth.

Let thirst be guide

Myth: Your water needs can be satisfied only by water.

Reality: Coffee, tea, soft drinks, fruit juice, milk, even beer and other alcoholic beverages, can be counted toward our daily total. The food we eat, from bread to broccoli, also contains water that can be counted.

“While drinking water is a frequent choice for hydration, people also get water from juice, milk, coffee, tea, soda, fruits and vegetables and other foods and beverages as well,” said Dr. Lawrence Appel, chairman of the panel that wrote the report and professor of medicine at Johns Hopkins University in Baltimore. “Moreover, we concluded that on a daily basis people get adequate amounts of water from normal drinking behavior — consumption of beverages at meals and in other social situations — and by letting their thirst guide them.”

In foods, water comes not only from fruits and vegetables, which are known to contain lots of it, but also from less obvious items.

“What percentage of a piece of white bread do you think is water?” Valtin asked. “The way to find out is to take a piece of bread and weigh it, let it sit out for two or three days while it loses all its water and weigh it again. It’s a very significant percentage.”

The institute said beverages containing caffeine and alcohol — thought by some to cause excessive loss of water and nutrients through urination — counted toward the body’s daily intake. Valtin advised caution on alcohol, saying “no scientific studies have been done on that.”