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A complete guide to staying hydrated before, during and after a workout

July 07 2023 5 min read

Whether you’re a serious athlete or simply like to keep fit and healthy, proper hydration is key when working out. 

But it can be easy to underestimate how much hydration can actually affect your workout. It doesn’t help that there are so many contradictory statistics about how much water we’re meant to drink each day and how frequently.

So, what are we supposed to believe?

We’ve enlisted the help of our expert Fitness First personal trainers to answer some of the most important questions about getting your hydration on track and how it can help you progress in your fitness journey.

How do you stay hydrated during exercise?

Water makes up about 60% of your body's weight, so it plays a vital role in your daily bodily functions. 

When you’re working out, you can lose a lot of fluid, so making sure that you’re “properly hydrated pre and post-workout is just one component of great exercise.” 

If you’re doing a moderate amount of exercise — say for an hour or so — then “drinking just water is fine. However, if you’re training for longer than an hour, a sports drink, squash, or water with electrolytes can keep you going for longer.”  

What are the effects of dehydration on the body?

You’d be forgiven for believing that only considerable dehydration can have a detrimental effect on exercise; we’re talking headaches, excessive perspiration and general aches.

But did you know that a mere 2% reduction in fluids can result in a 10-20% degradation in performance? That means your performance can be sapped even when you don’t feel dehydrated at all.

Does hydration affect the way you work out?

As sweat evaporates from your skin, it removes heat from your body and causes bodily fluid loss. Essentially, you need to drink fluid during your workouts to replace the fluids you lose when you sweat.  

“Even minor percentages of dehydration can cause major differences in your performance during training. Being dehydrated can lead to:

  • Dizziness
  • Nausea
  • Fainting
  • Higher fatigue rates
  • Heat stress

The tell-tale signs of dehydration are thirst and dark-coloured urine. It can also cause digestive issues and constipation and can even make you feel hungrier because a dehydrated brain confuses hunger and thirst. When you spot any of these symptoms, your body needs some water.”

Staying hydrated is easy, so when you work out just make sure you have a trusty bottle of water by your side! 

How much water should I drink per day?

The amount of water you should drink daily depends on several variables, not least the level of activity you plan to undertake. For example, a marathon runner will have different requirements from somebody doing a 30-minute weights session in the gym.

The weather can also make a big difference since you’ll sweat a lot more in warmer conditions.

However, general guidelines suggest that you should drink at least 2 litres of water per day. You should increase this by 500ml per hour of intense training, and increase this again if you tend to sweat a lot when you exercise.

How much water should I drink before exercising?

This is where a lot of people run into issues. Most people are good at taking water to the gym as a mid-workout refreshment, but it’s actually even more important to make sure you’ve topped up your fluid levels before your session.

You're most dehydrated when you wake up, so start the day with a glass of water and avoid coffee if possible. Having drinks regularly throughout the day will make a massive difference in your energy levels by the time you’re ready to work out.

Staying hydrated when you’re exercising might be easier said than done, but it’s imperative that you don’t allow your levels to dip. A short water break between sets or during quick breaks from cardio can help stave off exercise-induced dehydration, keeping you at your best for consistently high performance.

An easy way to ensure you get enough water is to set a timer — on your phone or watch — to go off every 15 minutes as a reminder to rehydrate. This is especially important if you’re doing exercise over a long period of time, such as training for a marathon and need to keep your fluid levels up.

How much should I drink during a workout?

During your workouts, “you should be drinking around 750ml of water or fluid — but this will entirely depend on the workout you’re doing and its level of intensity. For example, you’ll need a higher water intake for a long-duration cycle than you would during a 30-minute weight set.”

If you are becoming thirsty during your workouts, make sure not to drink too rapidly, as this can cause discomfort, make you feel bloated and affect the overall outcome of your workout. 

What should I drink after a workout?

While many of us fail to take hydration into account before our workouts, even more of us let ourselves down after an exercise session.

Drinking 50% more fluid than you lost through sweat will help to boost your recovery. The fastest way to recover is sipping small amounts of water regularly, rather than guzzling down litre after litre in one go.

You should also ensure that 20% of your water intake comes from solid foods. Opting for foods that are naturally high in water content — like cucumbers, tomatoes and celery — can help you recover more quickly post-workout.

Should I be drinking water or a sports drink when I workout?

While water is best to replenish hydration, intense workouts can often benefit from something that offers more energy. 

“If your workout is very much performance-based, long in duration and you sweat a lot, then it would be great to consider an isotonic sports drink that’ll help to maintain your body’s electrolytes.” 

Due to the amount of glucose and caffeine in them, sports drinks can provide your body with the burst of energy it needs to get through your workout. But, a lot of the time they also include a carb solution, so depending on your goals, these can either be beneficial to your progress.

How do I know if I’m not drinking enough?

Failing to drink enough water during the day can cause a whole host of problems for your mental and physical health. But, what are some of the telltale signs that you actually aren’t drinking enough?


Not drinking enough water can cause overall fluid loss in the body. Because of this fluid loss, you’ll notice a decrease in blood volume that puts excess pressure on the heart when trying to deliver oxygen and vital nutrients to our organs and muscles. 

“Lack of water causes you to experience extended periods of fatigue and low energy, as your body scrambles to find something else to make your body function without enough water.”

Decreased urination

When your body is dehydrated, the kidneys will start to retain as much fluid as they can to maintain their functions. This in turn will then “decrease the number of times you need to urinate. When you do go to use the bathroom, you’ll most likely find that your urine looks darker in colour, has a strong odour and looks cloudy in appearance.”

You may also be at a higher risk of a urinary tract infection (UTI) when your body lacks water, as there isn’t enough fluid to flush out toxins and bacteria.

Poor skin

“Water hydrates and plumps your skin cells to make your skin appear brighter, vibrant and more youthful. If you’re not drinking enough water, this can cause the skin to lose its plumpness and elasticity, leading to dryness, fine lines, wrinkles and even sagging skin.”

Water has also been known to help reduce acne and other skin problems by helping to flush out harmful toxins from the body.

Muscle cramps

Muscle cramps are a giveaway that you’re not hydrated enough. If you start to feel cramp coming on, take a break to have a drink. Don’t guzzle it down; instead, opt for short, small sips over a few minutes.

Once you’re refuelled, ease yourself back into your exercise, being careful not to overdo it: it can take a while for your muscles to fully rehydrate.

Dry mouth

One of the first signs of dehydration is dry mouth. As soon as your mouth starts feeling a little dusty, get a drink. Ignoring dry mouth can seriously impact your performance.


Feeling lightheaded during a workout is a sign of dehydration and a signal to take your workout down a notch.

Though willpower sometimes makes us want to push ourselves through a few more reps or another mile, feeling dizzy is an indicator that your brain isn’t getting the oxygen it needs. You should stop exercising the moment you feel dizzy; powering through a dizziness spell can be dangerous.

Can dehydration really impact my mood?

Being even mildly dehydrated can alter a person's mood, so it’s not just the physical effects it has on the body but it’s also the impact on your mental wellbeing too.

“Dehydration depletes the levels of amino acids in the brain, leading to increased feelings of anxiety, irritability and anger. On top of this, it also causes fatigue, headaches and difficulty in concentration, making it harder to perform basic tasks.”

With all of these mental emotions mixed into one, it can be a recipe for disaster. 

How much water is too much water?

Every day, we lose water through breathing, perspiration, urine and bowel movements. For our body to function properly, we need to replenish its water supply by eating and drinking anything that contains water. But, is it possible that we could sometimes drink too much?

“Any amount that starts to negatively affect your performance during exercise, or any more than 900 ml per hour can, over time, cause hyponatremia.” 

Hyponatremia occurs when the concentration of sodium in your blood is abnormally low. Since sodium is an electrolyte, it helps to regulate the amount of water that’s in and around our cells, as well as helps with blood pressure control.

Some common signs of hyponatremia include:

  • Nausea and vomiting
  • Headaches
  • Confusion
  • Drowsiness, loss of energy and fatigue
  • Restlessness and irritability
  • Muscles weakness, spasms and cramps

In more severe cases or left untreated, it can cause seizures, comas and even death.

What are the health benefits of drinking water?

Water is crucial in our everyday health, and here are some of its best benefits to encourage you to reach for your bottle of water more often are:

Helps maximise physical performance

If you don’t stay hydrated, then your physical performance is going to suffer — this is particularly important if you’re taking on exercises with higher intensity, like HIIT training.

“When you’re working out, it isn’t uncommon for people to lose as much as 6-10% of their water weight via sweat. So, if you exercise intensely and tend to sweat, staying hydrated can help you perform at your absolute best.”

Cushions the brain and spinal cords

When you’re dehydrated, you can affect your brain's structure and functions — with prolonged dehydration leading to problems with a person’s thinking and rationale. “Drinking enough fluid helps to cushion the brain, spinal cords and some of your body's other sensitive tissues.”

Helps to lubricate the joints

Water helps to create synovial fluid, a thin layer of fluid that cushions and delivers nutrients to the joints. 

“It also helps to reduce friction when you move your joints, meaning that you can push yourself that little bit further during your workouts!”

Boosts skin health

With dehydration, your skin is prone to becoming dull and vulnerable to breakouts, wrinkles and more!

“Drinking water daily helps to give the skin a brighter appearance, as when you’re dehydrated your eyes and cheeks can appear ‘sunken’ and skin loses its plumpness.” 

Get your hydration right with Fitness First

At Fitness First we have a wide range of classes, personal training sessions and more available for you, no matter your fitness level. 

To experience our fantastic facilities and meet our team of experts, book a free club visit at Fitness First today.

If you’re looking for some more inspiration, check out The Inside Track to read up on the latest fitness and nutrition advice from the expert personal trainers at Fitness First.