Ask a Dietitian: How Much Water Do I Really Need to Drink Each Day?

With the weather warming up, it’s more important than ever to ensure you’re drinking enough water every day and staying hydrated. But, what exactly does that mean? Below, we explain exactly how much water you should be drinking every day and why it’s so dang important to ensure you're getting an adequate water intake.

Why is water so important for our health?

The human body consists of 60-70% water. It’s no wonder then that water is the most essential nutrient for life. Water performs a myriad of vital functions, including as a solvent, a thermo-regulator, a building block, a lubricant, a reactant, a shock absorber and as a carrier of important nutrients to cells and removes waste away from them. Water also helps prevent kidney stones, aids digestion, prevents constipation and helps keeps your heart healthy.

Adequate water intake is essential to maintain hydration and water balance – the fine balance between water intake and water lost through the lungs, kidneys, bowels and skin. The adult human body is very clever at regulating body fluids however, children and the elderly may fail to receive thirst messages, which makes them more vulnerable to water imbalance and dehydration.

Negative water balance, caused by excess water lost through activity and/or heat leads to dehydration, triggering thirst. Excess water is excreted as urine from the kidneys to maintain water balance. Excessive water intake, on the other hand, stretches the stomach and expands blood volume, which signals the brain to stop drinking. Water intoxication, which is rare, can cause confusion, convulsions and at worst, hyponatraemia (where serum sodium levels are dangerously low) and even death.

How much water do we need to drink every day?

It’s important to meet our daily water requirements to avoid dehydration and negative health consequences. The truth is that we should be guided by our own thirst! The most common advice we hear is to drink 8 glasses of water per day (or 2 litres per day (L/day)). However, to be specific, the Australian Dietary Guidelines recommend adequate intake (AI) of water is: 3.4L/day for men 2.8L/day for women This is 8-10 cups of water/day. However, keep in mind that 25% of water is received through food intake and 75% through water intake as well as beverages such as milk, juice, tea and coffee.

Our individual water needs vary, depending on:

• How sedentary or active we are on any given day
• Our body composition and metabolism
• How much we exercise Our diet
• The climate we live in

For example, a sedentary individual may only require 1.5L/day. On the other hand, people who engage in regular physical exercise need to consume more water to compensate for water lost through sweating.

Pregnant Women and Children

Children, depending on age and gender, require 4-6 cups of water/day (1.4L/day – 2.2L/day) where 30% of water is said to come from food. Pregnant women should consume 2.3L/day of water or 9 cups per day, which represents a 10% increased requirement due to the needs of the growing baby.

Older Adults

The guidelines do not specifically recommend the elderly drink more water than younger adults. However, as kidney function declines with age, and their receptors don’t detect thirst as readily, this group of society are more vulnerable to dehydration. Therefore, more care should be taken to maintain hydration, to prevent constipation and cognitive impairment, as well as more serious complications such as stroke and to limit the risk of falls.

Active Adults

Active or sporty individuals require more water to maintain water balance. Water intake guidelines for elite athletes cannot be generalised, due to the myriad of factors that influence fluid lost during competition level physical activity, including the outdoor environmental conditions, the type of physical activity, duration and intensity and the opportunity to rehydrate, as well as individual factors such as genetic predisposition, sweat loss, availability of fluids and even beliefs regarding dehydration or over-hydration. Phew. However, as a general rule, keeping fluid intake up and careful planning of a ‘drinking strategy’ during intense exercise (and for several hours afterwards) to replenish water lost and maintain adequate hydration is essential, but it must be individualised and flexible.

What are the signs you’re not drinking enough water?

The first signs of inadequate water intake include thirst, fatigue, headaches, dry mouth, flushed skin and loss of concentration and appetite. Constipation can become a common problem if adequate hydration is not maintained. More severe dehydration can lead to difficulty concentrating, speech problems, extremity weaknesses, dizziness, exhaustion and dangerous extremes in blood pressure.

Tips for increasing water intake include:

• Keep a water bottle or jug of water at your desk and a water bottle in your car
• Make a habit of drinking water with dinner
• Use an App to track your water intake or set phone reminders
• Reduce coffee and tea through the day and replace with water instead
• Increase intake of fruits, vegetables and high-water content foods to increase water content through food

Always seek the guidance of your doctor or other qualified health professional with any questions you may have regarding your health or a medical condition.

Explore more content like this in our series, Ask a Dietitian.

Health & Performance Collective is the brainchild of Sydney Dietitians Jessica Spendlove and Chloe McLeod. They use their 20 years of combined knowledge and skills as dietitians to work with motivated people to live and perform at their best.

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