Updated 29 July 2015

Electrolytes and our ‘water balance’

Electrolytes are vitally important to our health: when the amount of water in our bodies changes, it can cause levels of electrolytes to become too high or too low.


Most people have heard about electrolytes, but probably don’t know what they are and why they are so vitally important.

To understand electrolytes we also need to understand the “water balance” of the body: When the amount of water in your body changes, it can cause your levels of electrolytes to become too high or too low. 


When we are born, up to 85% of our body weight is water. On the other hand, 70% of an adult body consists of water, and as people gain weight their bodies have more fat and less water. In obese individuals, only 45-55% of the body still consists of water. (Mahan et al, 2012)

12 interesting water facts

Needless to say, water plays an important role in every single action that takes place in our bodies, from blood circulation to waste elimination. Too little water leads to dehydration and death, but too much water can also cause fatalities due to “water intoxication”. In other words, maintaining just the right balance of water in our bodies is essential to our survival.


According to definition, electrolytes are “elements that dissolve in water and then disassociate into positive or negative ions.” (One negative ion can combine chemically with one positive ion to maintain a balance in the body.) (Mahan et al, 2012)

The most important electrolytes on the outside of the cells are sodium, calcium, chloride and bicarbonate. The most important electrolytes on the inside of the cells are potassium, magnesium and phosphate. Because some of these electrolytes on the outside and the inside of the cells are positive and some are negative, it is important that they are present in the correct concentration to control how much water moves in and out of the cells and that there is no build-up or deficiency of any one of the electrolytes on either side of the cell wall which would lead to health problems.

Who is at risk of dehydration?

Although they all play a role in maintaining the correct balance in our bodies, probably the two electrolytes that are the most important, and which can cause the most problems, are potassium and sodium.


We have been hearing a lot about sodium and particularly about how we should reduce our salt (sodium chloride) intake. Regulation No. R. 214 of the Foodstuffs, Cosmetics and Disinfectants Act, 1972 (Act 64 of 1972), published in March 2013, has set the ball rolling to reduce the sodium intake of the South African population (Government Gazette, 2013). While there is no doubt that South Africans eat too much salt, it is important to keep in mind that we do need enough sodium as an electrolyte to keep us alive. As this is so crucial to our survival, we will have an in-depth look at sodium in a future article.


Potassium is the most important positively charged ion inside the cells. It helps us to maintain a normal water balance; helps to maintain our acid-base balance; prevents dehydration; regulates the function of neurons in the nervous system; and helps our muscles to contract and relax. According to Mahan and her co-authors (2012), "Both hypokalaemia (potassium deficiency) and hyperkalaemia (excess potassium) can have devastating cardiac implications (i.e. prove fatal to the heart)".

What is potassium?                                                                                          

Sources of potassium are regarded as ubiquitous (found everywhere), and fruits, vegetables, fresh meat and dairy products are excellent sources of potassium. The following foods contain more than 300 mg of potassium per serving:


  • Avocado or spanspek (¼ of a small avo or spanspek)
  • Banana, 1 small
  • Dried fruit, ¼ cup
  • Mango, 1 medium
  • Pawpaw, ½ medium


  • Artichokes (1 medium)
  • Corn on the cob (1 mielie, fresh)
  • Dried, cooked or canned beans
  • Potatoes, baked in the skin (½ medium potato)
  • Spinach
  • Sweet potatoes
  • Tomato (fresh, or as tomato sauce or paste), 2 tablespoons
  • Butternut or winter squash
  • Coconut, 1 cup
  • Lasagne, 230 g
  • Milk, chocolate flavour, 1 cup
  • Milkshakes, 1 cup
  • Pizza, 2 slices
  • Soy milk, 1 cup
  • Spaghetti, 1 cup
  • Yoghurt, 170 g

Despite being so common in many foods, we can develop potassium deficiencies and also suffer from a build-up of excess potassium in the body, which can upset the acid-base balance of the body.

What potassium does for you

Next week we will have a look at sodium in greater detail, including why we need to reduce our intake, and address the problem that avoiding sodium totally can also be dangerous!

Read more:   

Your complete guide to potassium
What sodium does for you
Get your kids to drink more water                         


(Mahan KL et al. (2012). Krause’s Food & the Nutrition Care Process. 13th Ed., Elsevier, USA;

Image: Pouring water from bottle from shutterstock

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Dr Ingrid van Heerden is a registered dietician and holds a doctoral degree in Nutrition and Biochemistry. She believes that "we are what we eat" and offers free nutrition and weight loss advice via her DietDoc service on Read more of her articles.


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