SummaryRead the full fact sheet
- Water is essential to most bodily functions.
- The body has no way to store water and needs fresh supplies every day.
- The best source of fluids is fresh tap water.
- A child will need different amounts of fluid, depending on their age and gender.
- Women should have about 2 litres (8 cups) of fluids a day, and men about 2.6 litres (10 cups).
- People who are pregnant or breastfeeding need more fluid each day than usual.
- Dehydration can happen when the body’s fluids are low. It can be life threatening, especially to babies, children and the elderly.
The human body can last weeks without food, but only days without water.
The body is made up of 50 to 75% water. Water forms the basis of blood, digestive juices, urine and perspiration, and is contained in lean muscle, fat and bones.
As the body can’t store water, we need fresh supplies every day to make up for losses from the lungs, skin, urine and faeces (poo). The amount we need depends on our body size, , the weather, the food we eat and our activity levels.
Water in our bodies
Some facts about our internal water supply include:
- Body water content is higher in men than in women and falls in both with age.
- Most mature adults lose about 2.5 to 3 litres of water per day. Water loss may increase in and with prolonged exercise.
- Elderly people lose about 2 litres per day.
- An air traveller can lose approximately 1.5 litres of water during a three-hour flight.
- Water loss needs to be replaced.
Importance of water
Water is needed for most body functions, including to:
- Maintain the health and integrity of every cell in the body.
- Keep the bloodstream liquid enough to flow through blood vessels.
- Help eliminate the by-products of the body’s metabolism, excess electrolytes (for example, and potassium), and urea, which is a waste product formed through the processing of dietary .
- Regulate body temperature through .
- Moisten mucous membranes (such as those of the lungs and mouth).
- Lubricate and cushion .
- Reduce the risk of , such as by keeping clear of bacteria.
- Aid digestion and prevent .
- Moisturise to maintain its texture and appearance.
- Carry nutrients and oxygen to cells.
- Serve as a shock absorber inside the eyes, spinal cord and in the amniotic sac surrounding the foetus in .
Water in our food
Most foods, even those that look hard and dry, contain water. The body can get about 20% of its total water requirements from solid foods alone.
The process of digesting foods also produces a small amount of water as a by-product which can be used by the body. Water sourced this way can provide around 10% of the body’s water requirements.
The remaining 70% or so of water required by the body must come from fluids (liquids).
Recommended dietary fluid intake
How much fluid to drink each day
|Infants 0–6 months*
|Infants 7–12 months#
|0.8 litres total (with 0.6 litres as fluids)
|Girls and boys 1–3 years
|1 litre (about 4 cups)
|Girls and boys 4–8 years
|1.2 litres (about 5 cups)
|Boys 9–13 years
|1.6 litres (about 6 cups)
|Boys 14–18 years
|1.9 litres (about 7–8 cups)
|Girls 9–13 years
|1.4 litres (about 5–6 cups)
|Girls 14–18 years
|1.6 litres (about 6 cups)
|Men 19 years+
|2.6 litres (about 10 cups)
|Women 19 years+
|2.1 litres (about 8 cups)
|Pregnant girls 14–18 years
|1.8 litres (about 7 cups)
|Pregnant women 19 years+
|2.3 litres (about 9 cups)
|Lactating girls 14–18 years
|2.3 litres (about 9 cups)
|Lactating women 19 years+
|2.6 litres (about 10 cups)
* from breastmilk or formula
# from breastmilk, formula, food, plain water and other beverages
These adequate intakes include all fluids, but it’s preferable that the majority of intake is from plain water (except for infants where fluid intake is met by breastmilk or ).
Some people may need less fluid than this. For example, people:
- who eat a lot of high-water content foods (such as )
- in cold environments
- who are largely sedentary.
Other people might need more fluid than the amount listed and will need to increase their fluid intake if they are:
- on a , to help the kidneys process the extra protein
- on a to help prevent constipation
- vomiting or have , to replace the extra fluids lost
- physically active, to replace the extra fluids lost through sweat
- exposed to warm or hot conditions, to replace the extra fluids lost through sweat.
Although activity levels affect the amount of fluid needed, there are many factors that influence the fluid needs of athletes during training and competition. For example, it is likely that athletes exercising in mild conditions will need less fluid than athletes competing at high intensities in warm conditions.
How to get enough fluid in your diet
However, milk is about 90% water and is an important fluid, especially for children. Just remember to choose full-fat milk for children under 2 years old and low-fat and reduced-fat varieties for everyone else.
Tea can also be an important source of fluid. Tea can help you meet your daily fluid recommendations, and is a source of and polyphenols, which appear to protect against and .
If you prefer to get some of your fluids from fruit, aim to eat whole pieces of fresh fruit instead of having fruit juice – you’ll still get the delicious fruity juice (fluids) but you’ll also benefit from the bonus fibre and nutrients while avoiding the extra sugar found in fruit juice.
Tips for drinking more water
- Add a squeeze or slice of lemon or lime, or some strawberries or mint leaves to plain water to add variety.
- Keep a bottle or glass of water handy on your desk or in your bag.
- Drink some water with each meal and snack.
- Add ice cubes made from fresh fruit to a glass of water.
Limit mineral water intake
Limit the amount of mineral water or choose low-sodium varieties (less than 30 mg sodium per 100 ml).
If you prefer bubbly water, think about getting a home soda water maker so you can just use tap water and make it fresh when needed.
Fluoride in water
An additional benefit of drinking tap (reticulated or mains) water in Victoria is that, in most areas, fluoride is added to the water. Bottled water does not usually have good levels of fluoride.
Avoid sugary and artificially sweetened drinks
- sugar-sweetened and cordials
- fruit drinks
- vitamin-style waters
- flavoured mineral waters
- energy and sports drinks.
Having sugary drinks provides additional energy (kilojoules) to the diet, but no other essential nutrients. There is strong evidence of the association between having sugary dinks and excess in both children and adults, as well as and .
Artificially sweetened drinks add very little energy (kilojoules) to the diet and therefore do not contribute directly to weight gain. However, artificially sweetened drinks still maintain the ‘habit’ of drinking sweet drinks. They may also lead to decreased bone density (as people may drink less milk) and contribute to tooth decay due to their acidity.
Dehydration and water
Dehydration occurs when the water content of the body is too low. This is easily fixed by increasing fluid intake.
Symptoms of dehydration
Symptoms of dehydration include:
- mood changes and slow responses
- dry nasal passages
- dry or cracked lips
- dark-coloured urine
- confusion and hallucinations.
If dehydration is not corrected by fluid intake, eventually urination stops, the kidneys fail, and the body can’t remove toxic waste products. In extreme cases, dehydration may result in death.
Causes of dehydration
There are several factors that can cause dehydration including:
- not drinking enough water
- increased sweating due to hot weather, humidity, or
- insufficient signalling mechanisms in the elderly – sometimes, older adults do not feel thirsty even though they may be dehydrated
- increased output of urine due to a hormone deficiency, , or
- diarrhoea or vomiting
- recovering from .
Who is at risk of dehydration?
Anyone can experience dehydration but there are some people who can be more at risk, such as:
- the elderly.
Babies and children
Babies and children are susceptible to dehydration, particularly if they are ill. Vomiting, fever and diarrhoea can quickly cause dehydration.
Dehydration can be a life-threatening condition in babies and children. If you suspect dehydration, take your baby or child to the nearest hospital emergency department immediately.
Some of the symptoms of dehydration in babies and children include:
- cold skin
- dry mouth
- blue tinge to the skin (as circulation slows down)
- depressed fontanelle in babies (soft spot on top of the skull where the bones are yet to close).
Older people are often at risk of dehydration due to:
- changes to (declines with age)
- hormonal changes
- not feeling thirsty (body mechanisms that trigger thirst do not work as well as we age)
- medication (for example, diuretics and laxatives)
- chronic illness
- heat stress
- limited mobility.
Getting the right balance of fluid intake
Not drinking enough water can increase the risk of and, in women, urinary tract infections (UTIs). It can also lower your physical and mental performance, and your salivary gland function, and lead to dehydration.
But did you know that it is possible to drink too much water and cause a condition called hyponatraemia (water intoxication)?
Water intoxication (hyponatraemia)
Drinking too much water can damage the body and cause hyponatraemia (water intoxication), although it is rare in the general population.
Hyponatraemia occurs when sodium in the blood, which is needed for muscle contraction and sending nerve impulses, drops to a dangerously low level.
If large amounts of plain water are consumed in a short period of time, the kidneys cannot get rid of enough fluid through urine and the blood becomes diluted.
Hyponatraemia can lead to:
- blurred vision
- cramps (and eventually convulsions)
- swelling of the brain
- coma and possibly death.
For water to reach toxic levels, many litres of water would have to be consumed in a short period of time.
Many people believe that drinking water causes (or oedema). In fact, the opposite is true. Drinking water helps the body rid itself of excess sodium, which results in less fluid retention.
The body will retain fluid if there is too little water in the cells. If the body receives enough water on a regular basis, there will be no need for it to hold onto water and this will reduce fluid retention.
Where to get help
- , National Health and Medical Research Council and Department of Health and Aged Care, Australian Government.
- , Nutrient reference values for Australia and New Zealand, Australian National Health and Medical Research Council, and New Zealand Ministry of Health.
- ?, Mayo Clinic.
- , 2013, National Health and Medical Research Council and Department of Health and Ageing, Australian Government.