--- title: "How Much Water Do You Really Need to Drink Each Day?" id: "4315" type: "post" slug: "how-much-water-do-you-really-need-to-drink-each-day" published_at: "2025-01-07T09:11:56+00:00" modified_at: "2026-08-14T11:05:22+00:00" url: "https://www.allforone.com.au/how-much-water-do-you-really-need-to-drink-each-day/" markdown_url: "https://www.allforone.com.au/how-much-water-do-you-really-need-to-drink-each-day.md" excerpt: "Health & Performance · Education Eight glasses. Two litres. The enormous jug someone at work carries to every meeting. Hydration advice arrives as a number, and the number is almost never explained. So here is the Australian guidance in plain..." taxonomy_category: - "All in" --- Health & Performance · EducationEight glasses. Two litres. The enormous jug someone at work carries to every meeting. Hydration advice arrives as a number, and the number is almost never explained. So here is the Australian guidance in plain figures, how to work out roughly what your own body wants, and why thirst is a better guide than most people give it credit for. 4.9★★★★★4.9 across 260+ Google reviews. [Book a class](https://www.allforone.com.au/book-class/) [Call us](https://www.allforone.com.au/contact-us/) Physio-led strength, Pilates and spin classes at Yarraville and Hampton East. Coaching on your form included, every class. 01## How many litres of water should you drink a day? The short answer, for healthy adults in Australia: **about 2.6 litres of fluid a day for men, roughly 10 cups, and about 2.1 litres for women, roughly 8 cups.** Those are the adequate intake figures in the NHMRC Nutrient Reference Values, and they cover fluid of all kinds, not just plain water. Tea, coffee, milk, soup and sparkling water all go in the same column. Count the moisture inside your food as well and the numbers get larger again: total water intake sits at about 3.4 litres a day for men and 2.8 litres for women. The gap between those two sets of figures is your dinner. Food supplies roughly 20% of the water you take in, which is why fruit, vegetables, yoghurt and anything with a sauce quietly do part of the job for you. So the popular two litres is close to the mark for many women and a little light for most men, and it was never meant to be two litres of water on top of everything else you drink. It is also worth knowing what these figures are. They are population reference values, built from what Australians typically consume, not a daily quota you have failed if you miss. Pregnancy nudges them up, and breastfeeding nudges them up further again. Where they stop being useful is at the edges. A 55 kg office worker in a Melbourne winter and a 100 kg tradesman on a roof in February are both adults, and the same single figure cannot serve them both. That is where working from your own body weight helps. 02## How many ml per day, by body weight The common rule of thumb is **30 to 35 ml of fluid per kilogram of body weight per day**. Multiply your weight by 30 for the bottom of the range and by 35 for the top, and you have a personalised starting estimate in millilitres. **Worked example.** A 70 kg adult: 70 × 30 = 2,100 ml, and 70 × 35 = 2,450 ml. So roughly 2,100 to 2,450 ml a day, which is 2.1 to 2.45 litres. At 60 kg that becomes about 1,800 to 2,100 ml. At 90 kg, about 2,700 to 3,150 ml. **Now the honest part about where that rule comes from.** It is a clinical estimating tool, used to work out fluid needs for people in hospital and aged care, and it is not an Australian dietary guideline. The NHMRC figures in the section above are the official ones. The ml per kg rule is popular because it lands close to them at average body weights, and because it gives people a number that belongs to them rather than to the average of everyone. Treat it accordingly. It is a sanity check, not a quota. Older adults are usually estimated nearer 30 ml per kilogram and younger adults nearer 35. Very heavy or very light body weights push the calculation further from the reference figures than it deserves to go, because fluid needs do not scale neatly with size. And whatever the arithmetic says, hot weather, hard exercise, a bout of gastro or a long flight will move the real number around more than a few kilograms of body weight ever will. 03## Where the eight glasses rule came from The advice has been repeated for so long that it feels like it must have come from somewhere serious. It traces back to a 1945 US Food and Nutrition Board recommendation, which suggested adults take in around 2.5 litres of water a day. Reasonable enough. The trouble is the sentence that came next, which noted that most of that quantity is already contained in prepared foods and other drinks. That caveat got lost. What survived was eight glasses of plain water a day, stacked on top of your coffee, your tea and your lunch, with no allowance for body size, climate, activity or what you had eaten. A sensible total became a plain-water target that most people were never going to hit and did not need to. 04## What the water in you is doing Your body is about 60% water, and that water is not sitting there decoratively. It regulates your temperature, mostly through sweat. It lubricates your joints and keeps the discs in your spine plump. It carries nutrients around and supports digestion. It makes up the volume of your blood, which is why a hard, hot workout in a dehydrated state feels so much harder than the same work done well hydrated. And your brain notices before your muscles do: even mild fluid loss shows up as tiredness, headache and a shorter fuse for concentration. Which is also why one number cannot cover everyone. Age, body size, how much you move, how hot it is, what medications you take, whether you are pregnant or breastfeeding, and how much water is already in your food all pull your requirement around. Somebody eating salads, fruit and soup is starting from a different place to somebody living on toast. 05## Are you actually dehydrated? You will still see the claim that up to 75% of people are chronically dehydrated. It is repeated in a lot of good faith, and it does not hold up. There is no solid research behind that figure, and it appears to have escaped from a television news segment rather than a study. True dehydration is uncommon in healthy adults with easy access to a tap. It is genuinely more common in older adults, where the thirst signal weakens with age, and in anyone unwell with vomiting, diarrhoea or fever, which is one of the reasons [training after illness](https://www.allforone.com.au/training-after-illness-a-science-backed-guide-to-rebuilding-without-burnout/) needs a slower start than most people give it. Mild underhydration, on the other hand, is very ordinary. Air conditioning, a busy morning, a long meeting, forgetting the bottle in the car. It rarely announces itself dramatically. It turns up as a flat afternoon, a dull headache, dry mouth and work that takes longer than it should. **Two everyday checks handle almost all of this.** The first is thirst. For healthy adults it is a reasonably good regulator, and it deserves more respect than the drink-before-you-are-thirsty advice gives it. The second is colour: urine the shade of pale straw generally means you are fine, and consistently dark yellow suggests you are behind. A caveat on that one, because it catches people out: B group vitamins turn urine bright yellow regardless of your hydration, and some medications and foods change the colour too. The people who should not wait for thirst are older adults, anyone working or training in real heat, and anyone unwell and losing fluid. In those situations, drink to a plan rather than to a signal. 06## Can you drink too much water? Yes, and it is worth understanding rather than worrying about. Drinking well past what your kidneys can clear, usually large volumes over a short period, dilutes the sodium in your blood. The condition is called hyponatraemia, and it is rare, but it is real and it can be serious. Early signs are headache, nausea, bloating and confusion, and in severe cases it progresses to seizures. The situations where it shows up are fairly specific: endurance events where people drink at every station regardless of thirst, water-drinking challenges, and some illicit drug use. It is not something that happens to a person who had an extra glass with dinner. For healthy adults the protection is straightforward. Drink to thirst rather than to a target during long or hot efforts, take electrolytes or salty food alongside water when you are going for hours, and be sceptical of any advice that treats more litres as automatically better. Beyond what your body needs, extra water buys you nothing except trips to the bathroom. ### When a general rule is the wrong rule Fluid advice stops being general the moment there is a medical reason behind it. If you have heart failure, kidney disease or liver disease, or you take diuretics or other medications that affect fluid balance, your doctor may have given you a fluid target that is deliberately higher or lower than anything on this page. Follow theirs. The same goes if you are being treated for kidney stones, recurrent urinary infections or bladder symptoms, where the right intake is a clinical decision rather than a rule of thumb. Get emergency help, and call 000, if someone becomes confused, drowsy, is vomiting repeatedly or has a bad headache after drinking a large amount of water in a short period, particularly after a long event in the heat. Do not give them more water. Seek medical care the same day for signs of significant dehydration: dizziness on standing, a racing heart, very little urine over many hours, or a young child or older adult who is unwell and not drinking. 07## Do coffee and tea count? They do. Moderate caffeinated drinks count towards your daily fluid, and the old line that coffee dehydrates you is not supported at normal intakes. Caffeine has a mild diuretic effect, but the fluid arriving in the cup comfortably outweighs the extra you pass, and regular drinkers develop a tolerance to the diuretic effect anyway. A controlled trial that had habitual coffee drinkers alternate between coffee and water found no difference in their hydration markers. Herbal tea, milk, sparkling water and the water in soups and fruit all count too. Alcohol is the genuine exception, since it suppresses the hormone that helps you hold onto fluid, which is a fair part of why a big night feels the way it does the next morning. Sugary soft drinks and juices do hydrate you, but they bring a load of sugar with them, so they are not the place to make up a shortfall. 08## Training, sweating and hot days Exercise is the biggest single thing that moves your requirement. A reasonable starting point is an extra 500 to 750 ml for every hour of moderate to hard activity, and more when it is hot or humid. Use it to plan what to carry rather than as a quota to force down, and let thirst do the fine tuning on the day, because sweat rates vary enormously between people, from around half a litre an hour to well over two. If you want your own figure rather than an average, weigh yourself before and after a hard hour, ideally in minimal clothing. Roughly every kilogram lost is a litre of fluid gone, and it tells you far more than any calculator will. Do it after a [spin class](https://www.allforone.com.au/classes/spin-class/) and again after a [strength class](https://www.allforone.com.au/classes/strength/) , and you will usually find the two numbers are nothing alike. For anything long or genuinely sweaty, water alone can leave you short. Sodium is what helps you hold the fluid you drink, so an electrolyte drink or simply eating something salty with your water afterwards does more than another plain glass. And for most classes, most of the year, this is a small adjustment rather than a project: drink normally through the day, have your bottle with you, and top up afterwards. If you pull up sore the next day, that is about the training rather than the drinking, and [soreness is a poor measure of how well a workout worked](https://www.allforone.com.au/do-you-really-need-to-be-sore-after-a-workout-to-know-its-effective/) in any case. 09## Five things that make it easier **Start the day with a glass.** You have gone eight hours without drinking, so morning is the one time of day almost everyone is genuinely a little behind. It is also the easiest habit to attach to something you already do, like the kettle going on. **Carry a bottle you like.** The bottle is not magic. Having it in your line of sight is, because most under-drinking is forgetting rather than deciding. **Eat your water.** Cucumber, celery, lettuce, watermelon, strawberries, oranges, yoghurt and soup are all mostly water, and they arrive with the sodium and potassium that help you keep hold of it. Given food supplies about a fifth of your intake, this matters more than it sounds. **Give it some flavour.** Lemon, mint, cucumber or a few berries make plain water easier to keep drinking, which is the only feature that counts. **Anchor it to things you already do.** A glass with each meal, one when you sit down at your desk, one after class. Habits stacked onto existing habits survive; reminders on your phone mostly do not. Drink to thirst, check the colour, adjust for the day. 10## The version you can actually live with Use the Australian figures as your anchor: around 2.1 litres of fluid a day for women and 2.6 for men, with food quietly contributing about a fifth of your total on top. If you want a number that fits your own body, 30 to 35 ml per kilogram gets you close, as long as you remember it is a rule of thumb rather than a guideline. Then adjust for the actual day you are having, because a hot Saturday with a long ride in it is not a Tuesday at a desk. After that, stop counting and start noticing. Thirst and pale straw urine will tell you almost everything you need to know, and they update in real time in a way that no daily target can. The people who tend to get this wrong are not the ones drinking 1.9 litres instead of 2. They are the ones ignoring thirst all day, or forcing down litres they do not need because a number told them to. Hydration is one of the simpler inputs into feeling decent, alongside sleep, food and moving regularly. If the tiredness, headaches or heavy legs are not improving once the drinking is sorted out, that is worth looking at properly rather than drinking more water at. Our [physiotherapists](https://www.allforone.com.au/treatment/physiotherapy/) and our [physio-led classes](https://www.allforone.com.au/book-class/) share the same buildings, so the assessment and the training can be part of the same conversation. [Book a class](https://www.allforone.com.au/book-class/) ## Fill the bottle. Then go and use it. Book into a physio-led strength, Pilates, spin or yoga class at Yarraville or Hampton East, or call and tell us what you are training for. We will point you at the right class and the right starting point. [Book a class](https://www.allforone.com.au/book-class/) [Call us](https://www.allforone.com.au/contact-us/) FAQ## Questions we hear a lot How many litres of water should I drink a day?Australian guidance from the NHMRC Nutrient Reference Values sets adequate fluid intake at about 2.6 litres a day for men, roughly 10 cups, and about 2.1 litres for women, roughly 8 cups. That covers all drinks, not just plain water. Food adds roughly another 20% on top, which is why total water intake including food sits nearer 3.4 litres for men and 2.8 litres for women. These are population averages rather than personal targets, so climate, activity, body size, pregnancy and breastfeeding all shift them. How much water should I drink based on my weight?A widely used rule of thumb is 30 to 35 ml of fluid per kilogram of body weight per day. For a 70 kg adult that works out at roughly 2,100 to 2,450 ml, or 2.1 to 2.45 litres. It is worth being clear that this is a clinical estimating tool rather than an official Australian guideline, and it drifts away from the NHMRC figures at very high or very low body weights. Use it as a starting estimate and check it against thirst and urine colour. Does coffee count towards your daily water intake?Yes. Moderate caffeinated drinks count towards your daily fluid, and the idea that coffee dehydrates you is not supported at normal intakes. Caffeine is a mild diuretic, but the fluid in the cup outweighs the extra you pass, and regular drinkers become tolerant to that effect anyway. Tea, milk, sparkling water and soup all count too. Alcohol is the real exception, since it works against fluid retention. Can you drink too much water?You can, though it is rare. Drinking large volumes faster than your kidneys can clear dilutes the sodium in your blood, a condition called hyponatraemia, which causes headache, nausea and confusion and can be serious. It usually happens during endurance events or water-drinking challenges rather than in ordinary daily life. Drinking to thirst rather than to a target, and taking electrolytes during long or hot efforts, is the practical protection. Is 8 glasses of water a day right?It is not far off as a total, but it has been misread for decades. The advice traces to a 1945 recommendation of about 2.5 litres of water a day, which noted that most of that is already supplied by food and other drinks. The eight glasses version dropped that caveat and became eight glasses of plain water on top of everything else. Around 8 cups of fluid a day suits many women and around 10 suits many men. How do I know if I am drinking enough?For healthy adults, thirst and urine colour do the job. Urine the shade of pale straw generally means you are well hydrated, and consistently dark yellow suggests you are behind. B group vitamins and some medications turn urine bright yellow regardless, so allow for that. Older adults have a weaker thirst signal and should drink regularly rather than waiting to feel thirsty. How much extra water do I need when I exercise?An extra 500 to 750 ml per hour of moderate to hard activity is a reasonable starting point, and more in heat or humidity. Sweat rates vary hugely between people, from about half a litre an hour to over two litres. To find your own, weigh yourself before and after a hard hour, since roughly every kilogram lost equals a litre of fluid. For long or very sweaty efforts, add sodium through an electrolyte drink or salty food rather than relying on plain water alone. Are 75% of people chronically dehydrated?No. The claim is repeated widely but there is no good evidence behind it, and it appears to have started with a television news segment rather than research. True dehydration is uncommon in healthy adults with access to a tap, though it is genuinely more common in older adults and in anyone unwell with vomiting, diarrhoea or fever. Mild underhydration is common and shows up as tiredness, headache and poorer concentration.