15 Jun 2020

It is important that you drink enough during your recovery from critical illness. When we don’t drink enough, it can make us tired, dizzy, confused or give us headaches. If you are older, this might mean that you could have a fall or and your skin may be thinner. If we don’t drink enough, this is called being dehydrated. If you are dehydrated for a long time, it can lead to problems which might need medical treatment.

How can dehydration happen?

Dehydration happens when you use or lose more fluid than you take in.  As well as not drinking enough, things that can cause dehydration are:

  • being sick
  • having an upset stomach (Diarrhoea)
  • having a temperature (38C or more)
  • having diabetes that is not well controlled
  • sweating after exercise or during hot weather
  • medicines that make you wee more (called diuretics)
  • drinking too much caffeine
  • drinking too much alcohol. It is recommended not to regularly drink more than 14 units per week (14 units is equivalent to a bottle and a half of wine or five pints of export-type lager (5% abv) over a week)
  • difficulty in drinking enough, for example if you are confused and don’t want to drink or if you find it difficult to swallow. 

If you are finding it difficult to drink enough, speak to a healthcare professional.

The main way to know if you are dehydrated is if you feel thirsty.  Other signs to look out for include:

  • if your wee is dark yellow or smells strongly
  • if you wee less than you usually do, or don’t wee much when you do go to the toilet
  • feeling dizzy or lightheaded
  • having a headache
  • having low energy and feeling tired
  • having dry skin, mouth, lips or eyes.

Everyone needs different amounts of fluids every day, but as a rough guide, try to have 30-35 ml of fluids per kilogram of body weight per day. So, for a 70kg (11 stone) person this would be about 2000-2500ml (about 3.5 to 4.5 pints), whereas for a 50kg (8 stone) person this would be about 1500-1750ml (about 2.5 to 3 pints) a day.

If you are sweating more (e.g. in hot weather or after exercise) or have some of the risk factors for dehydration (see below), then you may need to drink more than this amount.

However, if a healthcare professional has advised you not to drink too much (for example, because of a medical condition), then you should follow their advice.

How can I drink enough?

Having enough to drink is important. These tips may help you:

  • Water is a great option, but you can drink other things as well. Liquid foods such as soup, ice cream or custard also help you get liquid in your body. However, remember that some drinks (fizzy drinks, fruit juice, smoothies) can be very high in sugar and should not be drunk too often, especially if you are concerned about weight gain or blood sugar control. You can add water to fruit juice down to make it lower in sugars.
  • Keep a reusable water bottle with you and sip it and refill it often. Some drinking bottles have markings on them to show you how much you could drink each hour.
  • Set yourself drinking goals each day, such as drinking a glass of water at the beginning of each hour, or a glass of water before each meal.


Drinking enough is important as it helps our bodies work well.  Try to drink enough each day, but if this is difficult or you are worried, please discuss this with your doctor.

Some more information you may find helpful:

British Dietetic Association Food Fact Sheets on:

NHS UK advice on:

See ICUsteps information for more information