Do You Need 8 Glasses of Water a Day? 7 Water Myths Busted

Water is essential, but there's a lot of folklore about how much we need and what it does for us. As a dietitian, I get asked about these all the time, so let's put seven common water myths to the test.

Myth 1: Do you really need 8 glasses of water a day?

Not exactly. There's no scientific basis for eight glasses as a universal rule, and researchers still haven't agreed on a single daily water requirement, because needs vary so much from person to person.¹ Your sex, age, body size, health, activity level and the weather all play a part.

As a general guide, Australian advice is about 10 cups (2.6 litres) of fluids a day for men and about 8 cups (2.1 litres) for women, plus an extra cup if you're pregnant or breastfeeding.⁶ That counts all drinks, not only water, and around a fifth of the water we need comes from food.

Some people need more specific advice: athletes training hard or for long periods, older adults (who may feel less thirsty), children, and people with kidney disease, heart failure or liver disease, some of whom are told to limit fluids.⁶

How to tell if you're drinking enough

Check your urine colour. Pale yellow or straw-coloured urine suggests you're well hydrated; darker yellow means it's time to drink more. Some medicines, vitamin supplements and foods can change urine colour for a few hours.⁶

Myth 2: Is drinking water with meals bad for digestion?

No. A common claim is that water with meals dilutes stomach acid and digestive enzymes. But your digestive system adjusts its secretions to the meal in front of it, and your stomach releases water along with acid and enzymes as part of normal digestion.

Liquids do leave the stomach faster than solids, but that doesn't stop solid food being digested. Drinking with a meal can also help soften food and move it along the oesophagus.

Myth 3: Does drinking more water flush out toxins?

Not in the way detox products suggest. Your body already removes waste on its own: the liver processes waste products, the kidneys filter the blood and pass waste out in urine, and the bowel clears waste from the gut. Water doesn't "cleanse" you, but these organs need enough of it to do their job.

Not drinking enough is linked with constipation, kidney stones and urinary tract infections.⁶ The evidence for drinking more is strongest in two groups:

• People who've had a kidney stone: drinking enough water to pass at least 2 litres of urine a day may lower the chance of another stone, although the evidence is low certainty.⁴
• Women with repeat bladder infections who drink little: in a 12-month trial, drinking an extra 1.5 litres of water a day roughly halved the number of infections.⁵

Myth 4: Does drinking more water give you clearer skin?

Probably not much, if you're already drinking enough. Dehydration can leave skin dry and less elastic. But a systematic review found only a handful of small studies on drinking extra water. Skin hydration rose slightly, mostly in people who drank little to begin with, and the overall evidence was weak.³ There's no good evidence that extra water clears acne or prevents wrinkles.

Myth 5: Water doesn't help with weight loss

It can help, mainly by replacing other drinks. A systematic review of six trials found that people lost weight when they increased their water intake, drank water before meals, or swapped kilojoule-containing drinks for water. Swapping sugary drinks for water worked best.² The studies were short and of low to moderate quality, so water is a helpful habit, not a weight-loss treatment on its own.

The easiest win is making water your usual drink instead of soft drinks, juice, cordial and sweetened coffees.

Myth 6: Water can't curb your appetite

Water before a meal adds volume to your stomach without any kilojoules, which may help some people feel full sooner and eat a little less. Pre-meal water was one of the strategies in the weight-loss trials above.² Sipping water during a meal is also a simple way to slow down and check in with how hungry you still are.

Myth 7: If you're thirsty, you're already dehydrated

Not quite. Thirst is your body's signal to drink, and feeling a bit thirsty doesn't mean you're dangerously dehydrated. Still, it's better not to rely on thirst alone. Australian advice is to drink regularly through the day, and more in hot weather or when you're active.⁶ This matters most for older people, whose thirst signal can be weaker.

Signs you need to drink more include dark urine, headaches, a dry mouth, tiredness and light-headedness.⁶

Frequently asked questions

Do you need 8 glasses of water a day?

Not necessarily. Australian guidance is about 2.6 litres of fluids a day for men and 2.1 litres for women, from all drinks, and needs vary with heat, activity and health.

Do tea, coffee and milk count towards your fluid intake?

Yes, all drinks count towards your fluids. Water is still the best choice, and caffeine can increase how much urine you pass.

Does drinking water help you lose weight?

It can help a little, especially when it replaces sugary drinks. The trials are short and of modest quality, so it works best as part of a wider eating plan.

What colour should your urine be?

Pale yellow or straw-coloured suggests you're well hydrated. Darker yellow means you should drink more.

Can you drink too much water?

It's rare, but drinking very large amounts quickly, such as during long endurance events, can dangerously lower sodium in the blood. People with heart, kidney or liver disease should follow their treating doctor's fluid advice.

References

Research (PubMed)

1. Armstrong LE, Johnson EC. Water intake, water balance, and the elusive daily water requirement. Nutrients. 2018;10(12):1928. PubMed 30563134
2. Bracamontes-Castelo G, Bacardí-Gascón M, Jiménez Cruz A. Effect of water consumption on weight loss: a systematic review. Nutr Hosp. 2019;36(6):1424–1429. PubMed 31657610
3. Akdeniz M, Tomova-Simitchieva T, Dobos G, Blume-Peytavi U, Kottner J. Does dietary fluid intake affect skin hydration in healthy humans? A systematic literature review. Skin Res Technol. 2018;24(3):459–465. PubMed 29392767
4. Bao Y, Tu X, Wei Q. Water for preventing urinary stones. Cochrane Database Syst Rev. 2020;2(2):CD004292. PubMed 32045491
5. Hooton TM, Vecchio M, Iroz A, Tack I, Dornic Q, Seksek I, Lotan Y. Effect of increased daily water intake in premenopausal women with recurrent urinary tract infections: a randomized clinical trial. JAMA Intern Med. 2018;178(11):1509–1515. PubMed 30285042

Australian guidelines

6. healthdirect Australia. Drinking water and your health. Last reviewed December 2025. View source

This article is general information and isn't a substitute for personalised advice. Speak to your practitioner about your situation.