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Water: are you drinking enough?

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We’ve all heard the advice ‘drink two litres of water every day’, but how much should you really drink? Dr Sarah Brewer reveals why we need to pay more attention to our hydration levels… 

Drinking enough water is one of the most effective - yet often over-looked - strategies for good health. No other nutrient is more essential, is needed in such large amounts, or has such a significant impact on your life when in short supply.

How much water do you need?
The official recommendation in the Government’s Eatwell Guide for UK residents is to drink six to eight glasses of fluid (including water, tea, coffee and juice) per day – although the size of the glass is undefined. Yet despite this, surveys show that more than half of us only drink between one and four glasses daily, with just one in ten meeting the recommended target.

The amount of water you need to replace your fluid losses varies from day to day. Typical fluid loss tends to be around two to three litres a day, but can be up to six litres if you take part in high-intensity exercise or you travel to a hotter climate. Athletes performing in hot climates may lose as much as 10 litres of fluid per day! To prevent dehydration during exercise, sip water regularly - every 20 minutes or so - especially if it is hot or you are at high altitude (to reduce the risk of altitude sickness).

What happens when you don’t get enough fluid?
The brain is particularly sensitive to dehydration, resulting in tiredness, poor concentration, reduced short-term memory, headache and mood changes such as agitation, impatience and feeling stressed.

Severe dehydration can impair sleep and increase the risk of constipation and kidney stones. It can also increase the thickness and stickiness of blood, leading to abnormal blood clotting that can precipitate a heart attack or stroke. And it’s not just older people who are affected. Summer heat can easily cause sweating and lead to dehydration, increasing the risk of heart attack and stroke, even in young adults. Lack of fluids, combined with excessive heat, can also lead to sunstroke.

Drinking too much water can overwhelm the kidneys and lead to swelling of the brain. Water intoxication is relatively rare, but can be dangerous. Stick to a target of no more than 2.5 litres per day.

Finding the balance
Your overall fluid balance is regulated partly by the concentration of salts, sugars and soluble proteins in your circulation, and by nerve receptors that detect the volume of fluid in the circulation. However, these regulators are not that sensitive and, by the time you feel thirsty, you are probably already dehydrated.

Studies involving people over the age of 65 have shown that fluid deprivation does not trigger sufficient thirst to restore fluid balance until dehydration has kicked in. One suggested reason is that older people tend to have a naturally higher concentration of salts in their blood due to reduced kidney function. This may cause the salt level needed to trigger thirst to reset to a higher point.

Loss of blood volume can also trigger thirst, but this reaction is even less sensitive - you can lose 10 per cent of blood volume without feeling the need to drink, hence the reason why you’re advised to drink lots of water before and after donating blood.

Urine colour is a useful way of checking your level of hydration. Aim for a pale, straw-like colour; if your urine is dark yellow and concentrated you should drink more fluids.

The benefit of electrolytes
When you lose fluid unexpectedly, i.e. through vomiting or diarrhoea, for example, you also lose electrolytes which need to be replenished. Electrolytes are mineral salts that dissolve to produce electrically charged particles. They are pumped in and out of cells, helping muscle fibres to contract and nerves to conduct messages.

The level of each electrolyte within your circulation is closely regulated by interactions between your lungs, liver and kidneys, endocrine glands and your nervous system. The body is normally pretty good at keeping blood levels of sodium and potassium within tight limits, but this can go awry as you age - especially if you are on medication such as diuretics, which disrupt electrolyte balance. Lack of trace electrolytes can lead to tiredness, fatigue, loss of energy, muscle aches and pains, and restless legs syndrome, and you may benefit from taking an electrolyte supplement.

Most electrolyte supplements, however, contain sodium which is already abundant in the diet. Excess sodium can lead to fluid retention and electrolyte imbalances. A zero-sodium electrolyte solution that provides important minerals such as potassium and magnesium, plus B vitamins needed for energy production, can help to enhance an active lifestyle and overcome fatigue.

NB If you are on diuretics check with a doctor or pharmacist that taking an electrolyte solution or supplement will suit your medication.


1. Water is the best thirst quencher and, if you are overweight, has the advantage of not supplying calories in the form of sugar.

2. Milk is a nutritious source of fluid and electrolytes if you can tolerate dairy products.

3. Tea is a popular drink that is low in calories and supplies beneficial antioxidants and some electrolytes. Although it contains caffeine, which is a mild diuretic, research shows that drinking tea provides more than enough water to offset this.

4. Herbal (non-caffeinated) teas are refreshing and an excellent source of fluid that counts towards your total water intake.

5. Coconut water is an excellent source of fluid as well as providing electrolytes to replenish those lost via the kidneys.

6. Some fluid comes from foods such as soups and juicy fruit, but water should form the main fluid source.

7. Avoid sugary, fizzy drinks and limit fruit juice and smoothies to a combined total of 150ml per day.

8. Drink fluids regularly throughout the day, rather than just drinking when you feel thirsty.

NB: People with certain heart and kidney problems may be advised to restrict their fluid intakes for medical reasons. Always follow your doctor’s advice.

The Nutrition Expert editorial team compiles articles with the help of Healthspan's experts to answer key questions from our community as well as researching common health topics and news.

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Nutrition Expert sources the latest information and advice from a range of qualified doctors, nutritionists and coaches. We always endeavour to have the most up to date information possible and publish new content weekly. However with the constant research in this field sometimes some of our older articles can become out of date. If you see anything that you believe needs to be updated please let us know via our Contact Us page