The “Eight Glasses of Water a Day” Rule Isn’t for Everyone
We’ve all heard it before: drink eight glasses of water a day to stay healthy. This simple guideline has become part of wellness advice, repeated by health gurus, fitness apps, and even medical professionals.
But is this advice more myth than fact? Recent research challenges the deeply ingrained “eight glasses of water a day” myth, suggesting this popular rule is neither as essential nor as accurate as many believe.
Where Did the “Eight Glasses of Water a Day” Myth Come From?
The “eight glasses of water a day” myth likely originated from a 1945 recommendation by the U.S. Food and Nutrition Board. They advised that an individual requires approximately 2.5 litres of water daily, equivalent to about eight cups. However, this recommendation included water from all sources—food, beverages, and drinking water. Unfortunately, this important detail was often ignored, leading to the oversimplified idea that one should drink eight glasses of water daily.
How did this myth become so widespread? The answer lies in the influence of health marketing and the bottled water industry. These industries seized on the simplified guideline, promoting it as a universal health standard. This tactic not only boosted bottled water sales but also entrenched the “eight glasses of water a day” myth in public consciousness, despite a lack of scientific evidence supporting the need for such high water intake.
Early misinterpretations of nutrition advice contributed to the myth’s longevity. For instance, in 1945, the U.S. National Research Council’s Food and Nutrition Board noted that “a suitable allowance of water for adults is usually 2.5 litres daily,” but they also mentioned that “most of this quantity is contained in prepared foods.” Over time, the nuance of this message was lost, and the recommendation became distorted into the “eight glasses of water a day” myth that persists today.
When speaking to ABC Australia, Dr. Pennie Taylor, a senior research scientist and clinical dietitian for the CSIRO, noted, “The study continues to validate and reconfirm what we know about water being essential for survival, and that the level of our daily water intake need is dependent on several factors: age, height, weight, general health, and environmental factors—weather, altitude, and humidity, for example.”
Is There Scientific Evidence for the “Eight Glasses of Water a Day” Myth?
Studies show that hydration needs are highly individual. Factors such as age, gender, body weight, physical activity, and environmental conditions all play a role. This variation means that a universal recommendation, like drinking eight glasses of water daily, is overly simplistic. It fails to account for these differences.
The notion that everyone should drink the same amount of water daily also overlooks the role of water-rich foods and other beverages. Foods like watermelon, cucumbers, and oranges contribute significantly to daily hydration. Beverages like tea and coffee also add to water intake. Strict adherence to drinking eight glasses of water daily is unnecessary for most people. Their hydration needs can often be met through a combination of these sources.
Are there Health Risks of Following this Myth?
While drinking water is essential for health, following the “eight glasses of water a day” myth without considering individual needs can sometimes be harmful. Contrary to popular belief, drinking excessive amounts of water does not necessarily provide additional health benefits. In fact, there is no strong evidence linking increased water intake with improvements in skin health, kidney function, or overall well-being in individuals who are already adequately hydrated.
Overhydration, or drinking more water than your body requires, can lead to a dangerous condition known as hyponatraemia. This occurs when the sodium levels in the blood become dangerously low due to an excessive intake of water. Symptoms of hyponatraemia range from nausea and headaches to more severe complications like seizures and, in extreme cases, even death. This condition is particularly risky for endurance athletes or individuals who consume large amounts of water in a short period.
How Does the “Eight Glasses of Water a Day” Myth Vary Across Cultures?
Studies have shown that hydration needs are highly individual and depend on a variety of factors. These include age, gender, body weight, physical activity level, and environmental conditions. This means that the idea of a universal recommendation, like drinking eight glasses of water daily, is overly simplistic and does not account for these crucial differences.
For example, a study published in 2022 explored how water turnover varies among different populations. The study examined over 5,600 individuals from 23 countries and found that water needs are influenced by factors such as body size, physical activity, and climate. The findings revealed that a young, active man in a hot, humid environment will require significantly more water than an older, sedentary person living in a cooler climate.
The suggestion that everyone should drink the same amount of water daily ignores the significant contribution of water-rich foods and other beverages to overall hydration. Dr. Taylor remarked, “We need more fluids if we are unwell, have increased needs for pregnancy and lactation, or have high-exercise levels.” Her observations highlight that factors like diet and physical condition play a significant role in determining how much water an individual needs, further debunking the necessity of the myth.
What Can We Learn from this Myth?
The myth serves as a reminder of how simplistic guidelines can sometimes overshadow the complexities of individual health needs. While general guidelines can be a useful starting point, they often fail to consider the wide range of factors that influence hydration, such as diet, climate, and personal health conditions.
Dr. Pennie Taylor, speaking to ABC Australia, explained, “This is where general guidelines can be helpful. They are simple enough to start someone on their way towards increasing their water intake, without complicating it. But guidelines can be too broad, and if a person is needing more or less—as they identify they are exercising more, become ill, or are pregnant—these changes may warrant being more precise.”
This shift towards more nuanced health advice can help ensure that people stay properly hydrated without falling into the trap of following outdated or overly simplistic guidelines.
References
- Valtin, H. (2002). “Drink at least eight glasses of water a day.” Really? Is there scientific evidence for “8 × 8”? AJP Regulatory Integrative and Comparative Physiology, 283(5), R993–R1004. https://doi.org/10.1152/ajpregu.00365.2002
- Negoianu, D., & Goldfarb, S. (2008). Just Add Water. Journal of the American Society of Nephrology, 19(6), 1041–1043. https://doi.org/10.1681/asn.2008030274
- Knechtle, B., Chlíbková, D., Papadopoulou, S., Mantzorou, M., Rosemann, T., & Nikolaidis, P. T. (2019). Exercise-Associated Hyponatremia in Endurance and Ultra-Endurance Performance–Aspects of Sex, Race Location, Ambient Temperature, Sports Discipline, and Length of Performance: A Narrative Review. Medicina, 55(9), 537. https://doi.org/10.3390/medicina55090537
- Yamada, Y., Zhang, X., Henderson, M. E. T., Sagayama, H., Pontzer, H., Watanabe, D., Yoshida, T., Kimura, M., Ainslie, P. N., Andersen, L. F., Anderson, L. J., Arab, L., Baddou, I., Bedu-Addo, K., Blaak, E. E., Blanc, S., Bonomi, A. G., Bouten, C. V. C., Bovet, P., . . . Speakman, J. R. (2022). Variation in human water turnover associated with environmental and lifestyle factors. Science, 378(6622), 909–915. https://doi.org/10.1126/science.abm8668
- Noakes TD, Goodwin N, Rayner BL, Branken T, Taylor RKN. Water Intoxication: A Possible Complication During Endurance Exercise. Wilderness & Environmental Medicine. 2005;16(4):221-227. doi:10.1580/1080-6032(2005)16[221:WIAPCD]2.0.CO;2
- Maguire, D. (2022, December 9). The “eight glasses of water a day” rule isn’t backed by evidence, so how much should we be drinking? ABC News. https://www.abc.net.au/news/2022-12-09/how-much-water-should-you-be-drinking-a-day/101742652
