Why water is essential: How much water do you really need and why?
- chandy Rodgers
- Jun 23
- 5 min read
Updated: 1 day ago
‘Light walking in warmer summer months can increase your fluid needs, as can swimming even though you are surrounded by water!’
Author: Chandy Rodgers
We know that staying hydrated is important, but there are lots of things that can affect how much water you need daily, and things you can do to reduce your risk of dehydration.
Questions this blog series will answer include:
In this article I will let you know if eight glasses of water a day is true and guide you through what affects how much water you need. Plus, at the end we will take a look at early signs of dehydration.
How much water do I really need and why?
Eight glasses a day - fact or fiction?
You may have heard it quoted that you should ‘drink eight glasses of water a day’. Is this true? The answer is sort of ‘yes’ and sort of ‘no’ - or more specifically ‘it depends’. First, what size is a glass? Think 8 x 8, that’s 8 x 8 fluid ounce glasses of water, or in today’s terms 8 x 240 ml of water—hence the suggestion of 2 litres. This is a good guide, but it is important to remember that we all have different needs. A healthy individual is thought to lose approximately 1.5 to 2 litres of water on average per day, before taking into account other factors.
What affects how much water you need?
Age: teenagers and adults generally need more water than younger children.
Gender: men often need slightly more water than women because of greater muscle mass.
Body size: bigger bodies require more hydration.
Breastfeeding: since breast milk is approximately 80% water, breastfeeding women are thought to lose approximately 700ml (about 25 ounces) and should increase their fluid intake accordingly.
Life stage: hormonal changes, menstruation, and hot flushes in menopause and peri-menopause can increase water loss.
Activity level: the more you move, the more you sweat, and the more water you lose. Light walking in warmer summer months can increase your fluid needs, as can swimming even though you are surrounded by water!
Climate: hot, dry, or humid weather makes you sweat more, even when you’re not aware of it.
Health & medication: fever, vomiting, diarrhoea, or even some medications (like diuretics) can all dehydrate you quickly.
What is the right amount of H2O?
As mentioned before, no one size fits all, but here is a rough guide to how much water you should be drinking on average per day before factoring in things that can affect your needs.
Women: around 2 litres per day (8–10 glasses)
Men: around 2.5 litres per day (10–12 glasses)
Teens: 1.5 to 2.5 litres per day, depending on age and activity
TIP: You don’t have to just drink water; some foods have a high water content, especially fruits and vegetables—think cucumber, celery and watermelon in particular. Herbal teas, milk, and broth-based soups are also a great way to get nearer your daily fluid requirements.
What increases your water requirements?
Apart from simply not drinking enough water, here is a closer look at things that can throw your fluid balance off and why:
Sweating
In hot weather or whilst exercising your body sweats in order to regulate your internal body temperature. As sweat evaporates from your skin, it removes heat from the body, but you also lose body fluid. The more you sweat the greater your need for water and electrolytes. NOTE: you might not always know you are sweating - a cool breeze on your body, swimming or wearing fewer clothes will all remove sweat quickly, so you might not notice how much fluid you are losing.
Illness
When you’re feeling under the weather, even if it’s just a mild bug or a bit of a fever, your body will lose more fluid than usual. You might sweat more (see above) or breathe a bit faster, especially with colds or flu, both of which can lead to water loss. Being off your food or not drinking as much as usual, will also impact fluid levels. Anything like diarrhoea or vomiting are other obvious causes of rapid fluid loss. Don’t drink large quantities at once to replenish lost fluids, but sip regularly throughout the day.
High salt or sugar intake
Eating too much salt or sugar can raise their levels in your blood, making your body work harder to bring things back into balance. One way it does that is by pulling water out of your cells to dilute the extra salt or sugar. Over time, this can make you feel tired, sluggish, or out of sorts. Your body will respond by making you feel thirsty, and your kidneys may also try to get rid of the excess salt or sugar through urine, which means you might end up peeing more and losing even more fluid.
Alcohol and caffeine
Caffeine and alcohol can both dehydrate you because they act as diuretics, which means they make your kidneys release more water through urine. With caffeine, this effect is mild unless you have a lot, but alcohol has a stronger impact as it stops your body making enough of the hormone that helps you hold on to water. So instead of keeping fluids in balance, your body flushes more out, which can leave you feeling thirsty, tired, or even headachy (think hangover from hell).
Poor diet
A diet full of ultra-processed foods can lead to dehydration because these foods are commonly high in salt and sugar (see above) and low in water and fibre both of which help your body stay hydrated. On top of that, additives can sometimes affect how well you absorb fluids, so even if you’re drinking enough, your body might not be using it as well as it could.
Early signs of dehydration
Have you heard the saying “if you feel thirsty you are already dehydrated”? Listening to your body’s cries for water can prevent more serious outcomes.
Symptoms of dehydration
feeling thirsty
having dark yellow, strong-smelling pee (urine)
peeing less often than usual (less than 3 or 4 times a day)
being constipated
feeling dizzy or lightheaded
headache
feeling tired and sluggish
a dry mouth, lips and eyes
muscle cramps
Signs of severe dehydration include: rapid heartbeat, confusion, sunken eyes, or extreme thirst. If you hit that point, rehydration becomes urgent and you should seek medical attention.
How do I stay hydrated, especially if I don't like water?
Click on the button below to read the final post in this series. I will share with you tops to stay hydrated, how to avoid forgetting to drink, what to do if you dislike water, how to infuse your water, guidance on filtering tap water and finally my top hydration checklist.
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