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If you can't stomach the thought of guzzling down eight glasses of water every single day, here's some good news: You're off the hook, more health experts are saying. 

A new editorial in an Australian public health journal is the latest to bust the widely-repeated health myth we need to guzzle 64 ounces, or eight 8-ounce glasses, of water each day just to stave off dehydration. Actually, we get enough fluids to keep our bodies adequately hydrated from the foods we eat and the beverages we drink -- even from caffeinated drinks like coffee and tea. 

Turns out, the whole "eight glasses a day" thing "really is no longer the recommendation; the recommendation is drinking to thirst," explains Madelyn Fernstrom, a board-certified nutrition specialist and TODAY's diet and nutrition editor. Drink when you're thirsty! What a novel idea.

It's not a bad idea to consume 64 ounces of fluid a day, but it's not a scientifically proven idea, either. It likely comes from a 1940s recommendation from the Food and Nutrition Board of the National Research Council, which said that adults should ingest about 2.5 liters of water a day. 

"But the often ignored second half of that statement pointed out that most of the water you need is in the foods you eat," explains Dr. Aaron Carroll, associate professor of Pediatrics and the associate director of Children's Health Services Research at Indiana University School.

"But that report wasn’t based on any solid evidence – it was just opinion," continues Carroll, who explored the waterlogged myth in the book "Don't Cross Your Eyes ... They'll Get Stuck That Way!", which he co-authored with Dr. Rachel Vreeman, assistant professor of pediatrics at Indiana University School of Medicine. "A number of years later, a famous nutritionist, Dr. Frederick Stare, said something similar about drinking eight glasses of water a day, but he, too, stated that it could be in the form of coffee, tea, milk, soft drinks, or even beer. He even said that fruits and vegetables are good sources of water."

But doesn't gulping down water help with weight loss? Kind of: It's true that drinking a high volume of water has been shown to work as an appetite suppressant, but consuming foods with high water content -- like watermelon, lettuce or grapefruit -- results in more weight loss than eschewing more foods for more (and more and more) water, writes the author of the Australian editorial, Spero Tsindos, of the department of dietetics and human nutrition at La Trobe University in Victoria. We've also heard that drinking lots of water helps ward off kidney stones and UTIs, but studies have shown that's only true for those who are prone to recurring episodes of either condition. 

Last summer, a paper published in the British Medical Journal grabbed headlines when it called the myth "nonsense" -- thoroughly debunked nonsense," for that matter, citing reports in 2002 and 2006 that couldn't find any "clear evidence from drinking increased amounts of water."

Yet the myth sticks around, likely because people have made a lot of money off the idea that we're all on the precipice of dehydration. (And we're definitely not -- government research on more than 15,000 people in 50 states show that over three years, the average American ingested 75 ounces of water a day, Carroll points out.)

"(B)ottled water and the entire health culture around drinking more water have been very lucrative," Vreeman explains. "Certainly, your body needs fluids and water is a healthy choice to meet those fluid needs, but many of us spend a lot of money, effort and guilt on forcing ourselves to drink more water than we really need."

So how much water should we be drinking? Whatever your body tells you it needs. Listen to your body, drink when it tells you to, and there's no need to drink more than that. (The idea that "when you're thirsty, you're already dehydrated" is another myth.) 

Fernstrom notes that it's of course better to choose water over sodas, sweetened juices or other sugary, high-calorie beverages. There may not be any evidence that excess water is doing you any good, but it's not likely doing any harm, either. 

"The issue of too much water, that's only a problem for extreme athletes who are sweating profusely and drinking too much water without replacing their salt," Fernstrom explains. For us mere mortals, if you drink lots of water throughout the day, "you're just going to pee it out," she says. "The worst that'll happen is you'll learn where more bathrooms are in your community."

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People with water-caused hives can drink liquids because the allergic reaction occurs only when the outer skin contacts water.

A few years ago, Dr. Alan Baptist, associate program director for allergy and immunology at the University of Michigan, faced one of the toughest allergy cases imaginable.

A young woman came to seek his help with migraine-like pain. Every time she came into contact with water she suffered headaches, along with reddish welts on her skin.

It turned out she was allergic. To water.

If you were allergic to water, how could you bathe? Or swim? A walk in the rain could turn into a painful afternoon. Yet some people truly are allergic to water, suffering with a condition known as aquagenic urticaria, or water-caused hives. The severity of the allergy varies widely, from barely noticeable to severe.

Aquagenic urticaria, first described in 1964, is very rare, although Baptist thinks it may be seriously underdiagnosed. “If a person showers every day and has urticaria every day, their doctor would think they just have chronic urticaria. Even many allergists aren’t going to be familiar with it.”

The body’s rejection of water is wildly counterproductive, mainly because we are made up mostly of water, our cells are filled with it and we can’t live without it. However, in almost all cases, the allergic reaction is ignited only when the outer skin contacts water. That’s how people with aquagenic urticaria can drink liquids and don't have an adverse reaction to their own cells.

But they can be allergic to their tears if they cry, and even their own sweat, Baptist explained. Fortunately, sweat typically doesn’t cause nearly as strong a reaction as diving into a pool.

Patients can be allergic to saliva, too. While a simple peck on the cheek or lips shouldn’t be much of a problem since symptoms generally depend on dose, you could pay a high price for very passionate kissing.

“Bathing is the biggest thing,” Baptist said. “Our patient tried to take very short showers and then dry off very quickly, but she still got the headaches, so she began showering only once every three days.”

It’s unclear what causes aquagenic urticaria and its source hasn’t been pinpointed. Because an outbreak releases large amounts of histamine, the mast cells involved in the body’s inflammatory response seem to be activated. How they are activated is still a mystery. The neurotransmitter acetylcholine is also released, so the nervous system must be perversely triggered, Baptist said.

Those facts point to treatment. While some have tried desensitization therapy – similar to how allergists sometimes treat kids allergic to peanuts -- results have been mixed. Baptist used a tool chest of drugs, including antihistamines and anti-cholinergic medications. Those didn’t suppress the patient’s headaches, so he added SSRI drugs typically used against depression.

“That got the headaches under control,” he said. “And we got the skin under control.”

She wasn’t cured of the allergy, but at least she can shower when she wants.

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