Dr Sarah Jarvis, MBE
Author: Dr Sarah Jarvis, MBE, General Practitioner (GP)

Dr Sarah Jarvis is the Clinical Director of the Patient Platform, an active medical writer, broadcaster, and the resident doctor for BBC Radio 2.

6 min read

You probably never give your kidneys a thought, but they’re hard at work for you 24 hours a day. They filter all the blood in your body 40 times a day through a million tiny filters and 140 miles of tubes. This lets them get rid of waste products and toxins, and balance the fluids and salts in your system. But keeping everything in your body in sync is hard work – in fact, your kidneys use ¼ of your energy.

Water bottle

How much fluid do I need?

Keeping your fluid intake up is essential for healthy kidneys. About 20-30% of your fluid comes from foods (especially fruit and vegetables); the rest comes from fluids you drink.

As a very basic rule of thumb, women need about 1600mls a day from drinks and men about 2000mls a day. However, you’ll need more if you’re in a hot climate; if you’re doing a lot of exercise; if you have a fever; or if you’re pregnant (pregnant women need about 1900mls a day) or breastfeeding (you need 2200-2300mls a day).

When you’re on holiday, you’re likely to be out of your usual routine and probably won’t have a kettle to hand. You may also be distracted and busy with new activities – so it’s easy to forget that you need to drink as much as usual, and more if it’s hot or you’re exercising. Even an air-conditioned environment can mean you speed up the rate you lose fluid, as sweat evaporates from your skin more quickly.

Are all fluids the same?

Water and non-alcoholic fluids all count towards your daily fluid intake. However, do bear in mind that sugary drinks contain a lot of calories, which can add up especially if you’re drinking more than usual.

You may have heard that caffeine-containing drinks make you lose water. In fact, this is only true if you drink a very large amount -  coffee and tea up to about 400mg caffeine a day (that’s about 8 cups of tea, 4 mugs of instant coffee or 4 cups of brewed coffee) count towards your fluid intake.

Alcohol, on the other hand, is a diuretic – it makes you pee more. So drinking alcohol makes you prone to dehydration. Do bear this in mind if you’re tempted to drink more alcohol than usual when you’re on holiday.

Drinking Water

How do I know if I’m dehydrated?

Your body should be producing about 1.5 litres of urine a day. Of course, nobody expects you to measure this, but the colour of your urine is a good guide. If you’re dehydrated, your kidneys reabsorb more water so your urine is more concentrated. You should aim to keep your urine pale straw-coloured – that means there’s enough fluid in your system.

The first things you’re likely to notice if you’re dehydrated are a dry, sticky mouth and feeling thirsty. Being dehydrated can also lead to tiredness and poor concentration; headaches; constipation and sometimes confusion. You’ll also be more prone to headaches and urinary tract infections. Not drinking enough fluids increases the risk of heat exhaustion and heat stroke, which is a medical emergency.

If you get dehydrated, common over-the-counter medicines like ibuprofen, along with lots of prescription medications, can damage your kidneys.

How safe is drinking water abroad?

We take it for granted in the UK that tap water – whether for drinking, washing vegetables or brushing our teeth – is safe to drink. That’s also the case in most of Europe, the USA, Australia and New Zealand. But if you’re outside these regions, there’s a risk that the tap water may not have been treated to the same standards as in the UK.

Drinking contaminated water can leave you at risk of traveller’s diarrhoea – one of the quickest ways to ruin any holiday. But other conditions, including hepatitis A, typhoid and cholera can also be passed on through contaminated food and water.

Top tips for water safety abroad

  • Bottled drinks with an intact seal should be fine.
  • Hot drinks made with boiling water should also be safe.
  • Boiling water (and keeping it boiling for 1 minute) is probably the most reliable way to purify water, but obviously, this isn’t always possible on holiday.
  • Water purification tablets definitely change the taste of water, but at least it’s safe and quick!
  • Specialist water purification filters designed to sterilise water are available in many travel equipment shops. Do make sure you confirm they’re designed to treat possibly contaminated water.
  • Domestic water filters made for use in the UK don’t work to remove germs from contaminated water.
  • If you wouldn’t drink it from a glass, don’t brush your teeth with it! Make sure you keep a supply of purified water in your bathroom.
  • Sticking to bottled drinks but putting local ice, made from local water, completely defeats the object. Avoid ice if in any doubt about the water supply where you’re staying.
  • Also, be aware that some foods can be contaminated because of their contact with contaminated water or other sources of infection. These include:
    • Raw or undercooked seafood or shellfish.
    • Ice cream made from unpasteurised milk
    • Salads and uncooked fruit and vegetables may have been washed in contaminated water.
    • Food standing at room temperature on open buffets (a feast for flies which are not the fussiest of consumers!)
    • Food from street traders that hasn’t been freshly cooked and served hot.
    • Unsealed bottles of mayonnaise.
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