How much water should I drink a day?

"Eight glasses a day" is the water rule everyone has heard. It's a reasonable place to start, but it isn't a fixed target, and the right amount for you shifts with the weather, how active you are and what else you eat and drink.

Here's what the Australian guidance says, what counts, how to tell whether you're drinking enough, and how the Thrive Health Band and app can help.

What the Australian guidance says

healthdirect is clear that there's no strict amount of water you should drink. As a general guide, it suggests:

Men: about 10 cups a day, or 2.6 litres.
Women: about 8 cups a day, or 2.1 litres, plus another cup a day if you're pregnant or breastfeeding.
Teenagers: 6 to 8 cups a day.
Children: about 4 to 5 cups a day.

In Australia a cup is about 250 mL. So the familiar eight glasses works out at about 2 litres, close to the guide for women and a little under the guide for men.

What changes how much you need

Those figures are a starting point. healthdirect notes that how much you need depends on things like the weather, especially hot or humid days, how active you are, how your body works and whether you have a medical condition.

With summer on the way, that first one matters. A long walk on a warm afternoon can leave you needing well over your usual amount. If summer nights also make sleep harder, our article on warm nights and summer sleep has some ideas.

What counts towards your total

You don't have to get it all from plain water. healthdirect says about one fifth of the water you need comes from food, and the rest from drinks. Milk, soup, juice, tea and coffee all count, though water is the best choice.

Tea and coffee bring caffeine with them, which is worth keeping in mind later in the day. The Sleep Health Foundation says caffeine's effects can last 3 to 7 hours, so an afternoon cuppa may be better as herbal tea if your sleep has been unsettled.

How to tell if you're drinking enough

The simplest check, according to healthdirect, is the colour of your urine. Pale yellow or straw coloured usually means you're well hydrated, and darker yellow means it's time to drink more. Some medicines can change the colour.

Feeling thirsty, a dry mouth, a headache or feeling light-headed when you stand up can also be signs that you need more fluid. healthdirect points out that older people may not notice thirst as readily, so if you care for an older parent, a gentle reminder to drink through the day can help.

If someone is severely dehydrated, for example very drowsy or confused, breathing fast or unable to keep fluids down, get urgent medical help, and call triple zero (000) in an emergency.

Can you drink too much?

It's very hard to drink too much water, healthdirect says, but it can happen. Drinking very large amounts during intense exercise, such as a marathon, can push the sodium in your blood too low. People with kidney, heart or liver conditions may not clear extra water as easily, so if your GP has given you a fluid limit, stick with their advice rather than a general number.

Small habits that help

A few of healthdirect's suggestions make water easier to reach for:

Keep it cold. A jug in the fridge is more inviting on a hot day.
Add flavour. Berries, a slice of lemon or other fruit make a change.
Mix it up. Sparkling water and herbal or iced teas, without added sugar, count too.
Carry a bottle. A refillable bottle makes it easy to keep water with you.

How Thrive helps you keep track

The Thrive Health Band has no screen and sits on a woven TPS strap. You see everything in the Thrive by Optihealth app, on iPhone or Android.

Water on the Nutrition tab. You can tap to add a glass as you go and see your total in millilitres, counting 250 mL a glass, towards a daily goal. The goal starts at 8 glasses and you can change it in your goals.
Body water from the Band. On the My Body screen you can take a body composition reading: rest a finger from your other hand on the electrode on top of the Band, over the Thrive logo, and tap Measure Now. Using bioimpedance, a tiny electrical current, it estimates your body water percentage in about 15 seconds. Readings can shift with what you've recently eaten or drunk and when you last exercised, so take them at a similar time of day. It's best read as a trend, and it isn't a diagnosis.
A hydration status score. On the Nutrition tab, Thrive brings your latest body water reading together with signals such as resting heart rate, sleep and activity, each compared with your own normal, into a score from 0 to 100. It's an estimate, not a count of what you've drunk, and a gentle prompt rather than a verdict. If your GP has given you a fluid limit, follow their advice rather than the score, and for signs of dehydration, see the section above.
A drink water reminder. You can set the Band to remind you to drink between a start and end time you choose, every 1, 1.5, 2, 3 or 4 hours.
Meals, Food Fit and Today's Load. Log what you eat, since food brings water too, and see from your steps and active minutes which days you've been busier.
Your own normal. Thrive learns what's usual for you across nine areas of your health, from what the Band measures and what you log, so changes in your sleep, energy or activity show up against your own history.

You can ask Ask Thrive questions in everyday language, such as "How many active minutes did I have each day this week?" or "How did my energy check-ins compare on my most active days?"

Thrive also keeps track right across your health, including sleep, blood tests, medications and supplements and your medical history. Ask Thrive can also help you get ready for a GP appointment. If you'd like a partner or carer to see it too, Thrive Loops lets you share selected information with a participating trainer, health professional or someone you trust. You decide what to share and with whom, and you can change or revoke access at any time.

Before you buy

You'll need a compatible iPhone or Android phone, because the Thrive app is on the Apple App Store and Google Play, in Australia and eight other countries. The app stores are only for downloading the app, though; they aren't where you buy the Band or a Plan. You can buy at thrivehealthband.com, or at a participating World Gym Australia location or health and wellness clinic.

The Thrive Health Band is A$660 for the first year under the launch offer (usually A$740). That includes the Band, which is yours to keep, and 12 months of the Thrive by Optihealth app, My Health on the web, Health Fingerprint, Ask Thrive, Thrive Loops and your data, paid once upfront. Prices are in AUD and include GST. Free Australia-wide shipping during the launch offer (usually A$14.99).

Nothing renews automatically. After your first year, you can get a new band plus 12 more months for A$660, or keep your band and renew the Thrive Connected Plan for A$240 a year (A$20 a month).

You're also covered by a 12-month Thrive Care Warranty, and consumer guarantees under Australian Consumer Law always apply. See Returns if something is wrong with your purchase.

Common questions

Do I really need 8 glasses of water a day?

Not exactly. healthdirect's general guide is about 8 cups (2.1 litres) of fluids a day for women and about 10 cups (2.6 litres) for men, and tea, coffee, milk and food all contribute.

Does coffee count towards my water intake?

Yes. healthdirect says tea and coffee count as fluids, though water is the best choice and caffeine late in the day can affect sleep.

Can I log water in Thrive?

Yes. In the Thrive by Optihealth app you can add glasses on the Nutrition tab towards a daily goal, and set a drink water reminder on the Band.

For more answers, see Questions.