With some experts now pouring water on the notion we need to drink eight glasses a day, dietitian Brooke Longfield looks at what you should know.
By the time you’re feeling thirsty, you’re probably already dehydrated. Our bodies consist of between 50 and 75 per cent water, and a loss of just one to two per cent of that signals dehydration, which can disrupt healthy body functions. Don't ignore the early warning signs.
Spot the signs of dehydration
Dry mouth: Perhaps the most obvious sign of feeling thirsty, this is a reminder that your body needs water. Rather than ignoring it, replenish your body with a refreshing glass.
Dark-coloured urine: If you’re healthy and well-hydrated, your urine should be a pale straw colour. Dark yellow or amber-coloured urine means you need to drink more.
Fatigue: Most of us put this down to stress or being under the pump with a heavy workload, but tiredness and lethargy can also be symptoms of dehydration.
Sallow skin: Long-term dehydration can lead to dry, flaky and wrinkled skin. The more you drink, the better the blood supply to your skin, which results in a healthy, glowing complexion.
Headaches: The brain is about 80 per cent water, so a telltale indicator that you’re dehydrated is a subtle headache. Before you take that painkiller, try quenching your thirst.
The juice of life
Water is what helps keep our blood circulating. Given that blood is 90 per cent water if you aren’t drinking enough your circulation becomes sluggish, making it less effective at providing your cells with oxygen. This means every part of your body, including your brain and muscles don’t function as well as they could.
You know that fuzzy, vague feeling you sometimes get at the end of the day? This can be caused by dehydration. Water lubricates the pathways between brain cells so when the brain doesn’t get an adequate supply you may have trouble concentrating.
Water also helps with digestion and prevents constipation. This can be a problem during the summer months when we sweat more and sometimes drink less. Without sufficient water, foods that are high in fibre become difficult for our body to digest, resulting in hard, difficult-to-pass stools.
Our bodies are constantly losing water. So where does it all go? We lose about 1.5L through urine each day (of course, this depends on how much water you drink). A normal amount of perspiration sees us lose around 200ml a day, with more on hot days, as this is the way the body cools its internal temperature.
We also lose water when exercising. During high-intensity exercise, a person can lose up to 2L of water in just one hour! However, low to moderate exercise results in minimal losses so unless it’s an extremely hot day, you probably don’t need to carry a water bottle with you on a gentle walk.
Perhaps less obvious, the simple act of breathing results in a considerable amount of water loss. Every breath you expel is a little water lost. Think of a cold morning when your breath looks like steam — this is water leaving your body and condensing into vapour. (Breathing while we sleep explains why we usually wake up in the morning weighing a little less and feeling thirsty!)
Surprising causes of dehydration
When we’re feeling exhausted and under pressure, stress can disrupt the production of the hormone aldosterone. This hormone helps regulate your fluid and electrolyte levels, triggering dehydration.
Herbal supplements such as dandelion, parsley and celery seed increase urine production and are used to treat fluid retention. Excessive use can cause dehydration, so watch the dosage.
Breastfeeding mums need an additional 700ml (about 2 cups) of water a day to replace the fluid lost in breast milk. A good idea is to keep a glass of water or a water bottle close by to drink while feeding baby.
Irritable bowel syndrome (IBS)
Diarrhoea is a common symptom of irritable bowel syndrome and can cause dehydration. (In fact, any gastro upset can.) So it’s vital to drink plenty of water or even an electrolyte-replacement drink such as Hydralyte to counter this.
Excessive thirst is one of the symptoms of untreated diabetes. When blood sugar levels rise, the kidneys attempt to remove excess glucose by producing more urine. This removes increasing amounts of water from the body, leading to thirst and dehydration.
How much is enough?
As a general rule, men need to replace around 2.6L (about 10 cups) of water a day, and women need 2.1L (about eight cups). This is where the rule about drinking eight glasses of water a day comes from. But it overlooks the fact that we take in a surprising amount of fluid through the food we eat.
Foods such as grapes, lettuce and watermelon are obvious examples. But even seemingly dry food like bread contains water, while foods cooked in water, such as rice or pasta, also add to your daily target. It’s estimated that the body gets around 20 per cent (between one and two cups) of its total water requirement from solid food alone, but exactly how much your daily diet contributes to your fluid intake is hard to calculate, so consider it more of a bonus to your water intake.
A natural flush
There is an element of truth in the claims of detox advocates who say drinking plenty of water helps flush out toxins. Our kidneys remove some of the toxic waste that is a by-product of our metabolism. These impurities are flushed out in our urine. A well-hydrated person has light coloured urine that signifies a lower concentration of toxins. Darker urine indicates the kidneys are holding onto fluid and that toxins are building up.
Water also helps keep our bowels moving regularly, which is another way our body rids itself of waste. So, a little extra water helps you feel better on the inside, too.
Is it possible to drink too much water?
Hyponatraemia is the rare condition when someone has too much water in their system. Excessive water can lead to the body's sodium (salt) levels falling dangerously low. This can cause all of our cells to swell, which can be especially harmful to the brain.
An excessive water intake is anything over four litres per day, unless it’s extremely hot or you’re an athlete. Even so, athletes are at risk of over drinking, especially if they try to rehydrate too quickly, resulting in what is known as water intoxication. Symptoms include blurred vision, nausea and vomiting. However, with 75 per cent of us chronically dehydrated, the chances are you’re drinking too little, not too much.
Every drop counts
Drinking water is the most effective and affordable way to rehydrate, but all liquids count in the daily tally — milk, juice, soup and even tea and coffee.
It’s a myth that tea and coffee don’t count. While these drinks have a mild diuretic effect — causing you to produce more urine — you ultimately get more fluid than you lose. Still, excessive amounts of caffeinated drinks can cause headaches and insomnia, so it’s best to keep your levels of caffeine to less than 400mg per day, which equates to about four cups of brewed coffee, or 4–13 cups of tea, depending on the strength.
Did you know?
A slice of bread is about 40% water.
You can lose up to 1.5L of water during a three-hour flight.
Drinking salt water will make humans sick.
We lose 1/2 cup of water each day just by breathing.