Why "Drink More Water" Is Bad Advice. Here's What the Science Actually Says

There's a good chance you've been told to drink eight glasses of water a day, carry a bottle everywhere, and sip constantly "just in case." It sounds harmless. It might also be the exact opposite of what your body needs, and the researcher who proved it happens to be South African.

Meet Dr. Tim Noakes, the Man Who Ruined "Drink As Much As You Can"

If you've run Comrades, or know someone who has, you've felt the influence of Tim Noakes without realising it. The Cape Town sports scientist spent decades studying what actually happens to endurance athletes on the road, and what he found upended the sports drink industry's favourite advice.

In the 1980s, Noakes and colleagues first identified exercise-associated hyponatremia: a dangerous drop in blood sodium caused not by dehydration, but by drinking more fluid than the body can actually handle (Noakes et al., Medicine & Science in Sports & Exercise, 1985). Two decades later, follow-up research case-proved it: hyponatremia in endurance athletes is caused by overdrinking, not sweat loss, directly reversing the "drink as much as you can" guidance that had dominated sports nutrition for years (Noakes, British Journal of Sports Medicine, 2006).

In plain terms: you can drink too much water. And for endurance athletes especially, it's a real, documented risk, not a fringe theory.

Your Sweat Is Not Like Everyone Else's Sweat

Here's something that should retire the "one sodium number fits all" approach for good: sweat sodium concentration ranges from roughly 10 to 90 mmol/L between individuals, shaped by genetics, heat acclimation, fitness level and diet (Baker, Sports Medicine, 2017). That's close to a tenfold difference between people. A generic electrolyte dose that works for one person might be wildly wrong for another.

This is also where exercise physiologist Stacy Sims' work becomes essential reading, particularly for women. Hormonal shifts across the menstrual cycle affect fluid and sodium balance, meaning hydration strategies built around male physiology don't automatically translate (Sims, ROAR, 2016). If you're a woman whose energy and thirst seem to shift through the month, that's not in your head. It's physiology.

So What Should You Actually Do?

Drink to thirst. That's genuinely the research-backed answer. Thirst is your body's real-time hydration signal, not a lagging indicator you need to outrun (Noakes, Waterlogged, 2012). You don't need to force litres "just in case" on a normal day.

Where electrolytes earn their place is during long, hot, or genuinely sweaty efforts, anything pushing past 60-90 minutes, or a day spent working outdoors in real heat. That's when a pinch of natural salt or a proper electrolyte mix, sodium, potassium and magnesium together, actually matters. Oversupplementing sodium without matching what you're losing isn't any more helpful than under-doing it (Baker, 2017). The goal is matching intake to loss, not maxing it out because a label told you to.

The Warning Signs Worth Knowing

Dark urine and genuine thirst mean drink. But swelling, nausea or confusion during a long effort can actually mean you've overdone the fluids, and that's a medical situation, not a "drink more" situation. It's worth knowing the difference, especially if you're training for anything longer than an hour or two in the heat.

The Bottom Line

If you train outdoors in South African heat, or you're doing anything over about 90 minutes, this actually matters for you. If you've been chugging litres out of habit rather than thirst, it's genuinely fine to relax and let your body tell you what it needs. And if you're a woman whose hydration needs seem to shift through the month, pay attention to sodium, not just water volume.

Hydration science has quietly moved past "drink more water." It's time the advice caught up.

This is general information, not personalised medical advice. Speak to your healthcare provider before changing your hydration or electrolyte routine, especially if you're pregnant, breastfeeding, or managing a condition like kidney or heart disease.

Sources

• Noakes TD, Goodwin N, Rayner BL, Branken T, Taylor RKN. "Water Intoxication: A Possible Complication During Endurance Exercise." Medicine & Science in Sports & Exercise, 1985.

• Noakes TD. "Case proven: exercise associated hyponatraemia is due to overdrinking." British Journal of Sports Medicine, 2006.

• Baker LB. "Sweating Rate and Sweat Sodium Concentration in Athletes." Sports Medicine, 2017.

• Sims ST, Yeager S. ROAR: How to Match Your Food and Fitness to Your Unique Female Physiology. Rodale, 2016.

• Noakes TD. Waterlogged: The Serious Problem of Overhydration in Endurance Sports. Human Kinetics, 2012.