Water is essential for life and it is very important to get the right amount of fluid to be healthy. However there are lots of mixed messages about how much, and what to drink and this can be confusing. Do I really need to drink 8 glasses of water on top of all my other drinks? Is it true that tea and coffee do not count towards my fluid intake? The answer to both these questions is no! The BNF ‘healthy hydration guide’ can help you choose a healthy balance of drinks.

This page also looks at why fluid is important, the effects of different drinks on health, and the needs of particular groups of people in the population. The information here is generally for healthy adults.

Why do you need water?
Your body is nearly two-thirds water and so it is really important that you consume enough fluid to stay hydrated and healthy. If you don’t get enough fluid you may feel tired, get headaches and not perform at your best. ‘Fluid’ includes not only water from the tap or in a bottle, but also other drinks that give you water such as tea, coffee, milk, fruit juices and soft drinks. You also get water from the food you eat – on average food provides about 20% of your total fluid intake.

How much do you need?
The amount of fluid you need depends on many things including the weather, how much physical activity you do and your age, but European recommendations suggest 1.6L of fluid per day for women (about 8 200ml glasses) and 2L  of fluid per day for men (about 10 200ml glasses). This is on top of the water provided by food you eat. You can get water from nearly all fluid that you drink, apart from stronger alcoholic drinks such as wine and spirits. 

Can you drink too much?
Yes – drinking excessive amounts of fluid is not helpful and, in rare cases can be dangerous. If you are passing urine frequently and your urine is very pale, you may be drinking more than you need.

Does it matter which drinks you choose?
When you choose your drinks it is important to be aware that although they all provide water and some also contain essential vitamins and minerals, they may also provide energy (calories). These calories contribute to your daily calorie intake in the same way as those from the foods you eat. It is also important to look after your teeth, and consuming sugar-containing drinks too often can potentially harm your teeth, especially if you don’t brush teeth regularly with fluoride toothpaste. It is also important to be aware that some drinks are acidic (e.g. fruit juice and carbonated drinks) and that this may cause dental erosion (damage to tooth enamel) if they are consumed frequently. For children, the use of a straw lessens the contact with teeth.

 

  • Drinking water is a great choice because it delivers fluid without adding calories or potentially damaging teeth.

  • Drinking tea or coffee also delivers water, and even though these drinks can contain caffeine, in moderate amounts caffeine doesn’t affect hydration. Pregnant women are advised to consume no more than 200mg or caffeine a day. This is equivalent to about two mugs of instant coffee or about two and a half mugs of tea. Other hot drinks such as herbal teas, hot chocolates and malted drinks can provide water. If these drinks are sweetened with sugar it increases their calorie content. The sugar also increases their potential to damage teeth if good dental hygiene is not practiced.

  • Milk contains lots of essential nutrients such as protein, B vitamins and calcium, as well as being a source of water. However, it can also contain saturated fat and so it’s a good idea for adults and older children to choose semi-skimmed (less than 2% fat), 1% or skimmed milks. For children between the ages of one and two years, the recommended milk is whole milk. From two years onwards semi-skimmed milk can be introduced gradually. Skimmed and 1% milks are not suitable for children until they are at least five years old because they have less vitamin A and are lower in calories.

  • Fruit juices and smoothies give you water plus some vitamins, minerals and natural plant substances from the fruit. Smoothies may also contain pureed fruit, which adds fibre. These drinks can also count towards your 5-A-DAY. One 150ml glass of fruit juice counts as one portion, and smoothies that contain at least 150ml of fruit juice and 80g crushed/pulped fruit count as two portions. Because fruit juices and smoothies contain sugar (and therefore calories) and can be acidic, they can potentially harm teeth.

  • Soft drinks are a source of water but, if they contain sugar, this adds to your calorie intake and the sugar can potentially damage teeth if the drinks are consumed frequently. It’s a good idea to limit consumption of standard sugar-containing soft drinks and to choose lower sugar or sugar-free (low calorie) versions instead.

  • Alcoholic drinks contain water, but drinking alcohol increases the amount of water you lose as urine, so drinks with a high alcohol content, such as wines and spirits, are not the best choice to stay hydrated. Normal strength beers, lagers and ciders also cause an increased loss of water as urine. However, because they are more dilute, drinking them causes a net gain in water overall. It is still important to keep alcohol consumption within the recommended limits (no more than 2-3 units per day for women and no more than 3-4 units per day for men).

  • Food - it may be a surprise to learn that we get on average 20% of our total water intake from food! Some foods have a high water content, especially fruits and vegetables, which are usually more than 80% water. Foods like soups and stews, which have lots of water added during preparation, also are a source of water. So food can provide extra water, on top of the 6-8 glasses of fluid you should drink a day.

 

How can I tell if I am getting enough water?
Your body has special mechanisms to make sure you stay hydrated. Feeling thirsty is your body’s way of telling you that you need to drink more. However, the easiest way to spot that you might not be getting enough water is if your urine is a dark yellow colour during the day. If you are getting enough water your urine should be a pale straw colour. So if it is darker than this or if you are urinating infrequently or passing very small amounts of urine, then you probably need to drink some more fluid. You also need to drink more if it is hot, or if your temperature is high due to physical activity or illness.

Do some people need more water than others?
Needs vary from one person to the next, but there are certain population groups who may need to pay particular attention to hydration.

  • Children need plenty of fluid, despite their smaller body size, and they should be encouraged to drink regularly, especially if they are very active. 

  • Infants get their fluids from breast or formula milk, but will start to get some fluids from food when they move onto solids.

  • Older adults may have a weaker sense of thirst and, if necessary, should be helped and encouraged to drink regularly. 

  • Physical activity also increases the amount of fluid you need to consume in order to replace the water you lose as sweat. Water is fine for rehydrating after the kind of moderate exercise that most active people choose, and the majority of active people do not need special sports drinks to stay hydrated. However, for high intensity exercise that lasts more than 40 minutes or so, drinks with a little added sugar and sodium (salt), such as sports drinks or home made versions, may be better at replacing the extra fluid lost as sweat.



The full BNF report on hydration and health is available here.

For a guide to healthy hydration for children aged 4-13 years, click here.

Last reviewed December 2013. Next review due December 2016.

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