Are you drinking enough water?

We’re told to drink at least eight glasses of water a day to stay healthy. But is that really enough? And does it have to be water, or do other fluids count?
 
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  • Updated:30 Sep 2001
 

01 .Introduction

Are-you-drinking-water

In brief

  • Water is essential to life — it’s possible to survive for more than 50 days without eating, but you can live only a few days without water.
  • You need about 2–3L of water per day to stay healthy — more if it’s hot, you’re sick, you’re exercising or working in air conditioning.
  • Thirst is an emergency response — by the time you’re thirsty, you’re already dehydrated.
  • There are many potential sources of water in our diet — soft drinks, tea, and many foods contribute to your daily water quota.
  • Alcoholic drinks are diuretic (they make you urinate more) — and if they’re stronger than 10% alcohol, you’ll lose more water than you take in.

Please note: this information was current as of September 2001 but is still a useful guide to today's market.

How do our bodies use water?

Our bodies consist mainly of water — 50–80% of your total body weight is water. Women typically have lower average body water content than men because they tend to have more body fat, which contains less water than muscle tissue.

And water is vital to all sorts of bodily functions. One key fluid — your blood — helps transport essential nutrients and oxygen around your body. Other fluids act as a lubricant for joints and eyes, help you swallow, act as a cushion for your nervous system, and help with waste disposal. On top of all that, water serves to regulate your body temperature — you sweat when you get too hot.

There are other ways in which water contributes to good health:

  • It maintains the health of your kidneys by helping flush toxins and body waste through them.
  • It reduces the risk of stones in your urinary tract (kidney stones or bladder stones).
  • Some preliminary research has shown that drinking plenty of fluid (particularly plain water) can reduce the risk of cancers of the colon and urinary tract (including kidneys and bladder) and breast cancer. However, more research is needed before definitive conclusions can be drawn.
  • It’s thought that drinking more water (but not fatty or sugary drinks) could help prevent childhood and adolescent obesity, partly because it creates a feeling of fullness and also because people sometimes mistake feeling thirsty for feeling hungry.
 
 

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02.How much water should I drink?

 

Your body continually loses water: in urine and faeces, through your skin and from the lungs (when you breathe out). This means you need to top up levels on a regular basis and drink enough to replace what’s lost.

Without perspiration, the normal daily turnover of water in adults is about 4% of body weight, which is 2.8 litres for a 70 kg person. However, the amount of fluid lost will vary from person to person because we’re all different — it will depend on your own particular metabolism, your state of health, your diet and how much exercise you do, for example. And some people are at greater risk of dehydrating.

According to a review published in the Journal of the American Dietetic Association, the average sedentary man should consume at least 2.9 L of water a day, and the average sedentary woman at least 2.2 L per day. About one third of this will come from food. In terms of how much you should actually drink, the Dietitians Association of Australia recommends the average adult drinks at least eight glasses (2 L) of fluid per day — more during hot weather and physical activity.

This doesn’t mean drinking glass after glass of plain water: there are plenty of other sources of water in your diet, however, it’s recommended your daily quota is made up of plenty of water: apart from anything else, it’s best for quenching your thirst, is cheap (or free) and contains no calories.

Drink more water if any of the following applies:

  • You’re exposed to high temperatures.
  • You’re carrying out strenuous work or physical activity — see below.
  • You’re exposed to air conditioning or heating for long stints.
  • You’re pregnant or breastfeeding.
  • You’ve got a fever, diarrhoea or been vomiting.

People at greater risk of dehydrating

The very young and the elderly are at greater risk of dehydration than most other people. It can result in heat stroke (extremely high body temperature) or heat exhaustion (excessive water and salt loss through sweat).

  • Babies and children up to four years of age are too young to respond to their bodies’ needs, and are particularly sensitive to the effects of high temperatures. Compared with adults, daily water loss is much greater in infants, at 15% of body mass — that’s about 1 L for a 7 kg baby.
  • While pregnant women require only an extra glass or so of water per day, nursing mothers need an extra 750–1000 mL above the basic recommendation.
  • Elderly people lose some of the sensation of thirst, so may not drink enough water to avoid becoming dehydrated. Another issue that adds to the risk is the inconvenience and embarrassment caused by incontinence and the need for frequent urination (people have been known to drink less than they should to avoid these problems).

Water and exercise

When you’re losing water rapidly, as you do when carrying out strenuous physical activity, you could already be dangerously dehydrated by the time your thirst mechanism kicks in.

A water loss of only 1% of body weight can impair physical and sporting performance during exercise, while a loss of 3–5% can diminish performance by around 20%. Apart from making you feel light-headed and nauseous, dehydration also increases muscle glycogen use, so you get tired faster.

Experts recommend:

  • You hydrate yourself two hours before exercising by drinking 400–600 mL — this allows time for adequate hydration and excretion of excess water.
  • Drink sufficient fluid during exercise to prevent dehydration from exceeding 2% of your body weight: small amounts (150–300 mL) every 15–20 minutes should do the trick.
  • To make sure you fully rehydrate after heavy exercise, weigh yourself before and after, and make up the weight loss in water.
  • For exercise that lasts less than 90 minutes, plain water is fine. For longer periods of exercise, a sports drink with glucose and electrolytes added may be beneficial.

Not enough or too much water?

So what happens if you don't drink enough water or you drink too much?

Not enough

A whole range of body processes works to keep your fluid levels relatively stable — the thirst mechanism and kidney function are just two. Generally, your total body fluid levels vary by less than 1%, regardless of fluctuations in what you drink. But there are dangers if you persistently drink too little.

  • It takes only small changes in your overall fluid levels to destabilise your system and bring about the symptoms of dehydration — as little as 1–2% of your body weight can do it. If you were 20% or more dehydrated, you’d die.
  • Early signs of dehydration include headaches, fatigue, loss of appetite, flushed skin, heat intolerance, light-headedness, dry mouth and eyes, a burning sensation in the stomach and dark urine with a strong odour.
  • If dehydration becomes more advanced, you may get symptoms such as difficulty swallowing, clumsiness, shrivelled skin, sunken eyes and dim vision, painful urination, numb skin, muscle spasms and delirium.
  • Of course long before these things start happening, a powerful thirst should kick in and persuade you to drink. And your kidneys are super-efficient at regulating water — if things get desperate, you’ll probably stop urinating.
  • If you’re not sure whether you’re getting enough water, a simple way to check is to keep an eye on the colour of your urine. It will be yellow first thing in the morning, but should become paler by mid-morning. If it doesn’t, you’re not drinking enough.
  • Don’t wait till you get thirsty to drink: thirst is actually an emergency response — you don’t become thirsty until you’re already dehydrated. The typical symptoms, such as a horrible taste, dry throat and cravings for cool wet liquid, are physiological responses your body uses to signal its dehydration.

Too much

It’s possible to drink too much water. Your body’s fluid balance can be dangerously upset if you drink more water than your kidneys can excrete. Your body cells swell, and you may feel drowsy, weak and suffer convulsions.

You’d need to drink more than six litres over a short period of time for this to be a danger, and you’d probably make yourself sick in the process. But it does happen: for example, several people have died from drinking too much water after taking the drug ecstasy.

If you’re not a big fan of plain (or even soda or mineral) water, the good news is you can meet your daily quota from a variety of different sources — both foods and drinks.

  • Fruit juice, cordial, soft drink and milk contain plenty of water, although if you drink over 2 L of these each day, you may be getting too much sugar and/or fat.
  • Although caffeine is a mild diuretic, evidence seems to be emerging that, for tea and coffee at least, the diuretic effect appears to be minimal if you drink them regularly and in normal strengths.
  • Alcohol is a stronger diuretic: as a rough guide, for every 1 mL of pure alcohol you drink, you lose 10 mL of water in urine. So, if you drink a 125 mL glass of red wine (12.5% alcohol) you’ll lose about 150 mL of water — a net water loss. If you drink full-strength beer (5% alcohol), you’ll lose about half the water, but the other half contributes to your daily water intake.
  • Food also contains water, from fruit and vegetables to chips and hamburgers.

Water in your diet

The table below shows typical figures for the water content of a range of common drinks and foods. It should give you some idea of good (and less good) sources of water in your diet.

Food / drink Portion size Water (mL)
Water (A) 250 mL 250
Soft drink 250 mL 235
Cordial (diluted) 250 mL 235
Orange juice 250 mL 230
Coffee (black) 240 mL (1 mug) 240
Coffee (white) 240 mL (1 mug) 235
Tea (black) 240 mL (1 mug) 240
Tea (white) 240 mL (1 mug) 235
Beer (lager) 375 mL (1 can / stubby) 350 (160) (B)
Beer (reduced alcohol, 2%) 375 mL 360 (260) (B)
Red wine 125 mL (1 glass) 110 (–40) (B)
White wine (dry) 125 mL (1 glass) 110 (–35) (B)
Apple 155 g (1 medium) 130
Banana 140 g (1 medium) 105
Watermelon 195 g (one cup) 180
Boiled potatoes 100 g 80
Roast potatoes 100 g 65
Baked beans 100 g 75
Cheeseburger 115 g 50
Meat pie 190 g 100
Hot chips 100 g 50
Macaroni cheese 300 g 200
Vegetable soup 300 g 270
Roast beef 200 g 130
Cheddar cheese 50 g 20
Cottage cheese 50 g 40
Milk (reduced-fat, or ‘Lite’) 200 mL 180
Yoghurt 200 g (1 pot) 165
Bread 30 g (1 slice) 12
Toast 27 g (1 slice) 7

Table notes

(A) Includes tap water, soda water and mineral water.
(B) The figure in brackets is the net water gain or loss, after taking into account the diuretic effect of allcohol.