Doctor Zac reveals how much water we should be drinking

An Aussie doctor has issued a warning as a huge trend involving major retailers such as Kmart influences how much we drink.

Welcome to Ask Doctor Zac, a weekly column from news.com.au. This week, Dr Zac Turner explains how much water you really need.

QUESTION: Hi Dr Zac, how much water should I be drinking in a day? I went to Kmart recently and I was shocked at how huge the water bottles are now. Is it possible to drink too much water in one day? I also noticed the 75 Hard Challenge expects you to drink a gallon of water every day, which equates to almost four litres. I thought the recommendation was two litres. Is this all a waste of time and too many trips to the toilet? – Chezzi, 46, Canberra

@kmartaustralia

Hydrate and feel great throughout the day with our big chugger water bottle, $18💧 #KmartAus#KmartFinds

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ANSWER: Thank you so much for a great question. In the age of oversized water bottles and viral fitness challenges, the question of how much water we actually need has become a hot topic.

Let’s dive into the science, the myths and what your body really needs.

How much water should you drink?

The old adage of “eight glasses a day” (about two litres) remains a reasonably reliable baseline for most adults. But the truth is, your water needs depend on factors like lifestyle, climate and health.

• The average adult: Two to three litres per day is ideal for most. This includes all fluids – yes, even your morning coffee counts.

• Athletes or active people: If you’re sweating through workouts, you’ll need closer to three litres, or even more.

• Climate counts: Hot, humid weather increases your fluid needs, while cooler days may not. So everyone up there reading this column in Cairns and Darwin, I’m looking at you.

So, unless you’re training for a triathlon, there’s no need to lug around a Kmart-sized jug.

An Australian doctor has issued a warning as a huge trend involving major retailers such as Kmart influences how much we drink.

The 75 Hard Challenge

The 75 Hard Challenge prescribes drinking a gallon of water daily – about 3.8 litres.

While that might work for bodybuilders or those with rigorous exercise regimens, it’s overkill for the average person. Drinking excessive amounts of water can lead to overhydration (or hyponatremia), a condition where your sodium levels are dangerously diluted.

Symptoms can include swelling, confusion and even seizures in severe cases.

Excessive water intake isn’t just unnecessary – it can disrupt your electrolyte balance and leave you running to the bathroom every half-hour. So stop it unless you’re really doing rigorous exercise.

Even your morning coffee counts towards your daily fluid consumption. Picture: iStock

Are mega bottles necessary?

Let’s be honest: the giant bottles trending in stores look more like workout equipment than hydration tools.

While they’re great for reminding you to drink throughout the day, you don’t need to hit their enormous capacities to stay healthy. In fact, using smaller bottles and refilling them often is a more practical – and less intimidating – approach.

Using smaller bottles and refilling them often is a more practical – and less intimidating – approach. Picture: iStock

Too much, too little: Spotting the signs

Your body is pretty good at telling you when you need more – or less – water. The key is to listen.

Signs you’re dehydrated:

• Dark yellow urine (think amber or cola colours)

• Dry lips, skin or mouth

• Fatigue, dizziness, or frequent headaches

• Constipation (hard, dry stools are a dead giveaway)

Signs you’re overhydrated:

• Frequent urination (if you’re running to the bathroom every 30 minutes, that’s a clue)

• Swollen hands, feet or face

• Nausea, confusion or irritability

A simple rule? Check your urine colour. Pale yellow is the goal. Anything darker means you need more water; anything completely clear means you’re likely overdoing it.

Water and your skin: The secret to looking fresh

Let’s talk about one of water’s more glamorous benefits – skin health.

Dehydration doesn’t just sap your energy; it also saps your glow. Fine lines, wrinkles and dullness are more pronounced when your skin is thirsty. In contrast, properly hydrated skin looks plumper, fresher and more youthful.

Water is great for your skin. Picture: iStock

A 2021 study in the Journal of Clinical Cosmetic Dermatology showed that individuals with higher water intake had better skin elasticity and fewer visible wrinkles. Think of water as the cheapest skincare product you’ll ever own – it works from the inside out.

So before you spend big on serums and creams, start with a glass of water.

The case for 2–3 litres

For most people, drinking two to three litres of water a day is plenty. It keeps your body functioning optimally without overwhelming your kidneys (or your schedule).

This amount includes fluids from food (like watermelon, cucumber and soups) and beverages like tea or coffee. Yes, caffeine lovers, your morning flat white counts.

The key is to spread your intake throughout the day. Chugging two litres at 9pm isn’t helpful – it’ll only guarantee midnight sprints to the bathroom.

A 3.7 litre water bottle from Kmart.

How to hydrate smartly

Not sure how to hit your hydration goals without overdoing it? Here are some simple tips:

Start early: Drink 500ml of water first thing in the morning to kickstart your metabolism.

Use variety: Add lemon, cucumber or herbal tea to make water more appealing.

Snack Smart: Foods like watermelon, celery and oranges are sneaky ways to boost your intake.

Monitor yourself: Aim for pale yellow urine and adjust based on activity or climate.

Spread it out: Sip water steadily throughout the day instead of binge-drinking it all at once.

If giant water bottles encourage you to drink more water, that’s a win. Just don’t feel pressured to match the latest Instagram trend by consuming more than you need.

Your body knows what it needs – listen to it.

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Dr Zac Turner is a medical practitioner specialising in preventive health and wellness. He has four health/medical degrees – Bachelor of Medicine/Bachelor of Surgery at the University of Sydney, Bachelor of Nursing at Central Queensland University, and Bachelor of Biomedical Science at the University of the Sunshine Coast. He is a registrar for the Australian College of Rural and Remote Medicine, and is completing a PhD in Biomedical Engineering (UNSW). Dr Zac is the medical director for his own holistic wellness medical clinics throughout Australia, Concierge Doctors.