Who Recommended Water Per Person Per Day? Unpacking the 8x8 Rule Myth

November 18, 2025 •

4 min read

The widely circulated recommendation to drink eight glasses of water per day is a decades-old piece of advice that has been widely misinterpreted over time. So, who recommended water per person per day, and is that guideline still a reliable measure for proper hydration? The real story traces back to past health reports that were later simplified, leading to a modern emphasis on personalized hydration needs.

Quick Summary

This article explores the historical origins of popular daily water intake recommendations, including the famous '8x8 rule'. It highlights how the nuances of early reports were lost and contrasts these with current, more personalized guidelines provided by major health organizations.

Key Points

8x8 Rule Origin: The popular rule came from misinterpreted health guidelines from 1945 and 1974 that included fluid from foods, not just drinking water.
IOM Recommendations: The Institute of Medicine suggests adult men consume about 13 cups (~3.0 L) and women 9 cups (~2.2 L) of fluid from beverages daily, recognizing total intake includes food.
Individualized Needs: Daily water requirements vary significantly based on factors like age, gender, body weight, physical activity, and environmental conditions.
Listen to Your Body: Thirst is a reliable indicator of initial dehydration for most healthy adults, while pale-yellow urine is a key sign of proper hydration.
Benefits of Hydration: Staying properly hydrated helps regulate body temperature, lubricate joints, deliver nutrients, and remove waste effectively.
Risks of Overhydration: Although rare, excessive water intake can lead to hyponatremia (low blood sodium), which is particularly a risk for endurance athletes.

The Origins of Water Intake Recommendations

Before the ubiquitous '8 glasses a day' mantra, historical advice on hydration was very different. In the early 1900s, it was commonly believed that athletes should drink little to no water during long-distance races, a practice now known to be dangerous. This was based on flawed observations that top performers often lost the most weight during races, leading to the false conclusion that dehydration was beneficial for performance.

The 1945 Food and Nutrition Board Report

The most direct origin of the modern water intake myth is a 1945 recommendation from the U.S. Food and Nutrition Board. This report stated, "A suitable allowance of water for adults is usually 2.5 liters daily." Crucially, a detail that was often lost in subsequent public messaging was that "most of this quantity is contained in prepared foods". The nuance that food contributes significantly to fluid intake was ignored as the years passed, leading many to believe that the full 2.5 liters must be consumed solely from drinking water.

Fredrick J. Stare and the 8x8 Rule

Another influential figure was nutritionist Dr. Fredrick J. Stare. In his 1974 book, Nutrition for Good Health, he suggested consuming "around 6 to 8 glasses per 24 hours," clarifying that this could come from various fluids, including coffee, tea, and milk, and that fruits and vegetables are also good sources. This advice, combined with the earlier 1945 report, contributed to the widespread and oversimplified 8x8 rule—eight 8-ounce glasses of water per day—ignoring the crucial context that other beverages and food count towards this total.

Modern Guidelines from Leading Health Authorities

Today, health organizations emphasize a more individualized approach to hydration, acknowledging that a one-size-fits-all rule is ineffective. Several authoritative bodies provide updated recommendations:

Institute of Medicine (IOM): A 2005 report established Adequate Intake (AI) levels based on a comprehensive review of fluid needs. The IOM suggests a total daily fluid intake from beverages of approximately 13 cups (~3.0 liters) for men and 9 cups (~2.2 liters) for women. This intake includes water from all beverages and foods, with roughly 20% typically coming from food.
World Health Organization (WHO): The WHO provides general guidelines for different populations and conditions. Their advice is often adjusted for factors like climate and activity level.
Mayo Clinic: Similar to the IOM, the Mayo Clinic emphasizes that fluid needs vary based on exercise, environment, health, and more. They acknowledge the '8 glasses a day' rule as a reasonable goal for most healthy people but stress that it's not a rigid requirement.

Factors That Influence Your Personal Water Needs

Your daily water requirement is not static. It depends on various physiological and environmental factors, including:

Physical Activity: Intense exercise increases fluid loss through sweating. For every 30 minutes of moderate exercise, you may need an additional 12 ounces of water.
Environment: Hot and humid weather increases perspiration, demanding higher fluid intake. High-altitude environments can also contribute to dehydration.
Health Status: Conditions like fever, diarrhea, and vomiting lead to significant fluid loss and require increased hydration. Urinary tract infections or kidney stones may also necessitate a higher fluid intake.
Pregnancy and Breastfeeding: Pregnant and breastfeeding women have increased fluid requirements to support their body's functions and milk production.
Age and Body Weight: Older adults may have a diminished sense of thirst, putting them at higher risk of dehydration. Body size also plays a role, with larger individuals generally requiring more fluid.

A Simple Formula for Estimating Water Needs

A good starting point for estimating your daily water intake is a simple formula: Multiply your body weight in pounds by two-thirds (or 0.67) to find your minimum daily ounces. For example, a 150-pound individual would need approximately 100 ounces (about 12.5 cups) of fluid. Remember to add more fluid for physical activity and adjust based on other factors. A simpler, common alternative is to drink water based on thirst cues and urine color. Pale yellow urine is generally a good indicator of proper hydration, while darker yellow indicates a need to drink more.

Comparison Table: Hydration vs. Overhydration


Aspect	Proper Hydration (Euhydration)	Overhydration (Hyponatremia)
Body's Status	Balanced fluid and electrolyte levels.	Excess fluid intake relative to electrolyte levels.
Primary Cause	Consistent fluid replacement throughout the day.	Drinking large amounts of water very quickly, especially during endurance exercise without replacing electrolytes.
Key Symptoms	Clear or pale-yellow urine, regular urination, good energy levels.	Nausea, headaches, confusion, fatigue, seizures in severe cases.
Risk Level	Generally low risk for healthy individuals.	Rare but potentially life-threatening.

Conclusion

No single individual or entity is responsible for universally recommending a rigid daily water intake for every person. Instead, the advice evolved from misinterpreted historical reports and was simplified into the easy-to-remember but inaccurate '8x8 rule'. Major health authorities today, like the IOM, provide nuanced guidelines that account for personal factors such as age, gender, activity level, and environment. The key to proper hydration is moving away from rigid rules and adopting a more personalized, responsive approach. Pay attention to your body's thirst signals and use simple indicators like urine color to guide your intake. This ensures you meet your individual fluid needs safely and effectively, promoting overall health and wellness. For more detailed information on hydration, consider consulting resources from reputable health organizations.

Resource for further reading: About Water and Healthier Drinks | Healthy Weight and Growth - CDC

Frequently Asked Questions

The rule is an oversimplification of early recommendations. Its origins can be traced to a 1945 U.S. Food and Nutrition Board report suggesting 2.5 liters of total fluid, a significant portion of which was meant to come from prepared foods, and a 1974 book by nutritionist Fredrick J. Stare.

Modern guidelines from the Institute of Medicine recommend an adequate fluid intake from beverages of about 13 cups for men and 9 cups for women. These are generalized estimates that include fluids from all beverages, not just plain water, and should be adjusted based on individual needs.

Yes, although it is rare for healthy individuals. Excessive, rapid water consumption can cause hyponatremia, a condition of low blood sodium levels that can be dangerous. This is most commonly seen in endurance athletes who overhydrate.

A person's daily water needs are influenced by their activity level, climate, overall health status, age, body weight, and whether they are pregnant or breastfeeding.

Common signs of dehydration include thirst, dark-colored urine, infrequent urination, fatigue, dizziness, and a dry mouth or lips.

Yes, moderate consumption of caffeinated drinks like coffee and tea contributes to your daily fluid intake. While caffeine is a mild diuretic, its effect is not significant enough to negate the hydrating properties.

The simplest method is to observe your urine color. Pale yellow or clear urine generally indicates adequate hydration, whereas darker yellow or amber urine suggests you need to increase your fluid intake.