Hydration: Myths vs Reality
Drinking water is simple, right? In reality, hydration is surrounded by myths stretching back decades that continue to spread today — often through health influencers and even some doctors.
Let us examine the 8 most common myths and what the science actually says.
Myth 1: "Drink 8 Glasses of Water a Day"
The belief: Everyone should drink 8 glasses (roughly 2 litres) of water daily.
What science says: Valtin (2002) published an extensive review in the American Journal of Physiology and concluded that this recommendation has no scientific basis.
The reality:
- Fluid needs vary enormously — depending on body weight, activity, climate, diet
- Much fluid comes from food (fruits, vegetables, soups)
- The "8 glasses" advice likely originated from a 1945 US nutrition recommendation, but that document noted most of this fluid would come from food
Myth 2: "Coffee Dehydrates You"
The belief: Coffee is a diuretic and therefore dehydrates the body. You should drink a glass of water for every cup of coffee.
What science says: Maughan et al. (2003) and subsequent studies have clearly shown that moderate caffeine intake does not cause dehydration.
The reality:
- Caffeine is a mild diuretic, but the fluid content of coffee compensates for this effect
- 3–4 cups of coffee per day are neutral from a hydration standpoint
- Regular coffee drinkers develop tolerance to the diuretic effect
- Coffee "counts" toward daily fluid intake
Myth 3: "Clear Urine Means Good Hydration"
The belief: Urine should be completely clear and colourless — this indicates good hydration.
What science says: Completely clear urine may actually indicate overhydration.
The reality:
- Pale yellow urine is ideal — it indicates normal hydration
- Completely clear urine means you are drinking more than necessary
- Dark yellow to amber — suggests dehydration
- Note: some vitamins (especially B2/riboflavin) turn urine bright yellow, which does not indicate dehydration
Myth 4: "Thirst Is Too Late a Signal"
The belief: If you feel thirsty, you are already dehydrated. Drink before thirst strikes.
What science says: For most people, thirst is a reliable indicator of fluid needs.
The reality:
- The thirst mechanism activates when body weight has dropped ~1–2% from fluid loss — this is a normal physiological response
- For athletes, cautious "pre-emptive drinking" is justified, but only during intense exercise
- In everyday life, responding to thirst is a perfectly adequate strategy
- Exceptions: older adults whose thirst mechanism may be weakened
Myth 5: "The More Water, the Better"
The belief: You can never drink too much water. More is always better.
What science says: Overhydration is real and potentially dangerous.
The reality:
- Hyponatremia — dangerously low blood sodium from excessive water intake — is potentially life-threatening
- Deaths have been documented at marathons, military exercises and even water-drinking contests
- The risk is higher during prolonged activity when only water is consumed without electrolytes
- Important: add sodium to water during prolonged activity
Myth 6: "Sports Drinks Are Better Than Water"
The belief: Sports drinks are always better than water, especially during training.
What science says: It depends on the situation.
The reality:
- Exercise under 60 minutes: plain water is perfectly adequate
- Intense exercise over 60 minutes: an electrolyte-containing drink is beneficial
- Hot conditions: electrolytes become more important even for shorter sessions
- For routine daily activity, water is the best choice — do not add unnecessary calories
Myth 7: "Water Cleanses the Body of Toxins"
The belief: Drinking lots of water "cleanses" the body and "removes toxins."
What science says: This is an oversimplification.
The reality:
- The kidneys filter blood regardless of how much water you drink (within limits)
- Excessive water intake does not speed up toxin removal
- The liver and kidneys do their job normally — they do not need to be "helped" with extra water
- Adequate hydration supports kidney function, but too much is too much
Myth 8: "Only Water Hydrates"
The belief: Only pure water counts toward hydration. Other drinks "don't count."
What science says: Maughan et al. (2016) published a study in the American Journal of Clinical Nutrition measuring the hydration index of different beverages.
The reality:
- Milk, tea, coffee, juice — all contribute to hydration
- Milk was actually one of the best hydration sources (due to protein and electrolyte content)
- Only high-alcohol drinks (spirits) are clearly negative for hydration
- Water in food (fruits, vegetables, soups) counts as well
Summary: What Should You Actually Do?
- Drink when you feel thirsty (sufficient for most people)
- Urine colour should be pale yellow
- Coffee and tea count toward fluid intake
- Add electrolytes during prolonged training
- Do not overdrink — overhydration is a real risk
Read more:
References
- Valtin, H. (2002). "Drink at least eight glasses of water a day." Really? Is there scientific evidence for "8 x 8"? American Journal of Physiology - Regulatory, Integrative and Comparative Physiology, 283(5), R993–R1004.
- Maughan, R. J., Griffin, J. (2003). Caffeine ingestion and fluid balance: a review. Journal of Human Nutrition and Dietetics, 16(6), 411–420.
- Maughan, R. J., Watson, P., Cordery, P. A., Walsh, N. P., Oliver, S. J., Sheridan, K., & Sheridan, F. (2016). A randomized trial to assess the potential of different beverages to affect hydration status: development of a beverage hydration index. American Journal of Clinical Nutrition, 103(3), 717–723.
- Noakes, T. D. (2012). Waterlogged: the serious problem of overhydration in endurance sports. Human Kinetics.
Disclaimer
Dietary supplements are not a substitute for a varied, balanced diet and healthy lifestyle.
