Staying hydrated: 6 real health benefits, and how much water you actually need
"Drink 8 glasses of water a day" is 1 of the most repeated health rules, and 1 of the least explained. How much do you actually need? What does water really do for you, and what's been oversold? This guide sets out the benefits with research behind them, the claims without it, and simple ways to tell if you're drinking enough.
How much water do you need?
The European Food Safety Authority recommends a total water intake of about 2 litres a day for women and 2.5 litres for men. That's total water, from all drinks and food, and food usually supplies around a fifth of it. So in practice most adults need roughly 1.6 to 2 litres from drinks: about 6 to 8 glasses, more in hot weather, when you exercise, or when you're breastfeeding.
Tea, rooibos, coffee and milk all count. Coffee's mild diuretic effect doesn't cancel out the water in it for regular drinkers. Sugary drinks count too, but they bring sugar you don't need, so water is the best everyday choice.
6 benefits backed by research
1. Sharper focus. A 2018 analysis of 33 studies found that dehydration measurably impaired attention, coordination and complex thinking. The effect was clearer once people had lost more than 2% of their body weight in fluid, which is easy to reach after a sweaty workout or a hot day with too little to drink.
2. Better physical performance. Muscles work harder and heart rate climbs faster when you're under-hydrated, especially in the heat. Our guide to exercising in a heatwave covers fluids for training.
3. Fewer kidney stones. This is 1 of the best-supported benefits. A 2016 analysis found that people who drank more fluid had a substantially lower risk of developing kidney stones, and of stones coming back.
4. Fewer bladder infections, for women prone to them. In a 2018 trial, 140 women who got repeated bladder infections and drank less than 1.5 litres a day added 1.5 litres of water daily. Over a year they had about half as many infections as the women who didn't.
5. Easier digestion. Fluid works with fibre to keep stools soft. If you're increasing fibre, increase water with it. Drinking extra water when you're already well hydrated won't do more.
6. Fewer dehydration headaches. Being short of fluid is a common headache trigger, and a glass or 2 of water often helps that kind of headache. The evidence that extra water prevents migraines is limited, so it's worth trying, but not as a replacement for treatment.
What water doesn't do
It doesn't "flush out toxins". Your liver and kidneys clear waste whether you drink 1.5 litres or 4. Drinking far more than you need just means more trips to the bathroom. It isn't a blood pressure treatment. Severe dehydration can make blood pressure drop, not rise, and if you have high blood pressure, the things that help are covered by your doctor's advice, not by your water bottle.
Signs you're not drinking enough
- Dark yellow urine, or going to the toilet fewer than about 4 times a day. Pale straw colour is the target.
- Thirst, a dry mouth, headache, tiredness or dizziness, especially on hot days.
- Cramps during exercise.
After 60, thirst becomes less reliable. Older adults can be low on fluid without feeling thirsty, so it helps to drink at set times: a glass with each meal and 1 in between.
Easy ways to drink more
- Keep a bottle on your desk or in the car, and refill it at set times.
- Start the day with a glass of water before your coffee.
- Have a glass with every meal.
- Flavour it: lemon, cucumber, mint, or cold unsweetened rooibos.
- Eat water-rich foods: watermelon, cucumber, tomatoes, oranges, soups.
Make your water bottle work twice
Our collagen peptides dissolve in cold water, iced rooibos or a smoothie, so your daily scoop can go into a drink you were having anyway. See the collagen range → Free delivery on orders over R800.
Frequently asked questions
Can you drink too much water?
Yes, though it's rare. Drinking very large amounts quickly, such as during long endurance events without replacing salt, can dangerously dilute the sodium in your blood. Drink to thirst, and include electrolytes on long, sweaty days.
Does coffee dehydrate you?
Not at normal intakes for people who drink it regularly. It counts towards your daily fluid.
Does drinking more water help your skin?
If you're dehydrated, your skin can look dull and feel dry, and drinking enough helps. Drinking extra beyond that hasn't been shown to improve skin. For what the research says about skin, see do collagen supplements really work?
I have a heart or kidney condition. Should I drink more?
Not without asking your doctor. Some conditions need fluid limits, not more fluid.
The sources
- EFSA Panel on Dietetic Products, Nutrition and Allergies (2010). Scientific opinion on dietary reference values for water. EFSA Journal 8(3):1459. View →
- Wittbrodt MT, Millard-Stafford M (2018). Dehydration impairs cognitive performance: a meta-analysis. Medicine & Science in Sports & Exercise 50:2360–2368. View →
- Cheungpasitporn W et al. (2016). Treatment effect, adherence, and safety of high fluid intake for the prevention of incident and recurrent kidney stones: a systematic review and meta-analysis. Journal of Nephrology 29:211–219. View →
- Hooton TM et al. (2018). Effect of increased daily water intake in premenopausal women with recurrent urinary tract infections: a randomized clinical trial. JAMA Internal Medicine 178:1509–1515. View →
Find out more
- How to exercise safely in a heatwave
- How much sugar is too much?
- What to drink for acid reflux
- Celtic sea salt: what it does and doesn't do
- How sleep improves your health
This article is general information, not medical advice. If you have heart, kidney or liver disease, ask your doctor how much you should drink.
About the author
Candy Hamilton is the owner of Health Nut, which has supplied collagen to South African homes and health shops since 2016. She holds a Certificate in Human Nutrition from Health Academy Australia (2020) and writes the research summaries on this site. Every study cited is linked so you can read it yourself. More about Health Nut →
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