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By: Andrew Forrest - July 2025
Proper hydration is crucial for safe walking and hiking. Water makes up about two-thirds of the human body and is vital for nearly all bodily functions.
Whether you're a casual park walker or a multi-day trail trekker, staying well-hydrated helps your heart circulate blood more easily, allows your muscles and joints to function smoothly, and helps regulate your body temperature.
On the other hand, even mild dehydration can quickly decrease your physical performance and mental alertness. In this guide, we will examine why hydration is crucial for walkers and hikers, how dehydration affects your body and mind, warning signs to look out for, effective hydration practices before, during, and after a hike, tips for multiple-day expeditions, and the role of electrolytes in possibly preventing cramps and fatigue.
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The information provided here is intended for general educational purposes only and should not be regarded as medical advice or a substitute for professional healthcare. If you are experiencing a medical emergency or serious symptoms, seek immediate assistance from a qualified medical professional or contact emergency services. Always consult your GP or a healthcare provider for personalised medical guidance and treatment.
Before beginning any exercise programme, especially if you are new to exercise, returning after a break, or have any existing health concerns, you should consult with your GP or a qualified healthcare provider. Always listen to your body and stop immediately if you feel discomfort, dizziness, or pain.
Even slight dehydration can surprisingly impact your hiking performance. Exercise science research indicates that losing approximately 2% of your body weight through fluid loss, which can occur after just one or two hours of strenuous hiking on a warm day, significantly decreases endurance and strength.
One study found that dehydration, caused by about a 2% loss of body water, led to a 10% reduction in aerobic performance during endurance exercise. A comprehensive meta-analysis of numerous studies also concluded that dehydration consistently diminishes endurance performance by around 2-7%, with greater declines seen at higher levels of dehydration.2,3
In practical terms, this means that if you're not drinking enough, you will likely walk more slowly, feel weaker, and tire more quickly than
you would when fully hydrated. Dehydration puts strain on your body by decreasing blood volume and making your heart work harder to circulate
blood.1
It can also impair your cooling system, primarily affecting your ability to sweat, as reduced water intake leads to a higher body temperature and a greater risk of overheating. The American College of Sports Medicine states that most research agrees that dehydration exceeding about 2% of body mass significantly reduces endurance and exercise performance.4
In summary, walking or climbing hills will feel more difficult than they should if you are even slightly dehydrated.
Although hiking mainly requires endurance, you often need short bursts of strength, such as navigating steep scrambles or lifting a heavy pack. Studies have shown that dehydration can also decrease muscle strength and power output.
For instance, a 2007 study observed a 3-5% decrease in muscle strength and power during high-intensity exercise in dehydrated
participants. You may also find exercise to be much more demanding when you are dehydrated.
Participants in one trial reported higher levels of exertion and fatigue when dehydrated compared to when exercising while well-hydrated, even at the same intensity. All these effects can combine to make a long walk or hike feel like a slog if you haven't been drinking enough.5
Water makes up about two-thirds of the human body and is vital for nearly all bodily functions. Hydration not only influences your muscles, but it may also affect your brain. If you've ever felt scatterbrained or irritable when thirsty, that's no coincidence. Our brains rely on proper hydration to function optimally, and dehydration can impair concentration, decision-making, and mood.
Research has shown that even mild dehydration, equivalent to around 1-2% of body weight, can start to impair cognitive performance. In
young men, for instance, 1.6% dehydration was found to increase errors in vigilance and slow down working memory tasks. Other studies involving
both men and women have observed that about 2% dehydration causes significant declines in attention, memory, and mood.6
In another study, volunteers who were approximately 2.8% dehydrated due to exercise and heat experienced a significant decline in reaction time
and short-term memory compared to when they were fully hydrated.7
Dehydrated hikers often report feeling more tired, easily confused, or less mentally sharp while walking. This could lead to navigation errors or safety mistakes if you're not well-hydrated, as hydration is crucial for concentration and good decision-making in the hills.
Mood can also suffer as mild dehydration has been linked with increased tension, anxiety, and fatigue. The key point is that drinking enough water helps keep your mind clear and your mood upbeat, which is just as vital as physical energy when out walking or hiking.8
Beyond performance, dehydration can pose health risks ranging from minor to severe. At the mild level, you might experience a dry mouth, headache, or cramps. As dehydration worsens, it can cause heat exhaustion or heat stroke (especially in warm weather), dizziness and fainting, or, in extreme cases, kidney issues. The good news is that serious outcomes are highly preventable, provided you recognise the warning signs and rehydrate promptly.
It's essential to listen to your body and spot dehydration early. Don't wait until you're about to collapse out on your walk - by recognising dehydration symptoms, you can drink before the situation worsens.
Early warning signs of dehydration include:1
If you notice any of these signs, do not ignore them. Pause and drink fluids - taking small, frequent sips is best. In most cases,
mild dehydration symptoms will improve within 10 to 15 minutes of rehydrating.
If someone is extremely dehydrated, such as being very disoriented, not urinating at all, or having a rapid pulse, it's an emergency, and you should seek medical help immediately. However, the aim is to prevent this from happening by staying hydrated consistently.
Preventing dehydration is much easier than treating it during a hike. By following a few simple hydration habits, you can maintain balanced fluid levels and avoid the performance dips and risks mentioned above. Here's how to stay hydrated before, during, and after your walk:
Start every hike or long walk well hydrated. Think of this as topping up your tank. On the day of your hike, drink plenty of fluids in the hours leading up to it. As a guideline, aim for about 500-600 ml of water in the 2-3 hours before you start, and perhaps another small glass (200-300 ml) 20 minutes before setting off.9
This ensures you start with your body's water reserves fully replenished. Don't gulp it all down at the last minute; instead, sip it gradually in
the lead-up to your walk, as you will then wee a lot of it out, rather than it being absorbed by your body. Also, be cautious with dehydrating
drinks. Go easy on alcohol the night before and caffeine on the morning of your hike, as these can increase fluid loss.
If you're preparing for a particularly long or strenuous hike (or it's a hot day), consider adding electrolytes to your pre-hike fluids. It is often recommended to drink about 500 ml of an electrolyte drink or water with an electrolyte tablet in the hour before a long hill walk or other extended endurance activity. The electrolytes help your body retain fluid more effectively and prepare you for sweat losses. In any case, do not start a hike already thirsty or dehydrated - it's difficult to catch up with hydration once you're out there.
This is where the real hydration battle is won or lost. While hiking, it is essential drink regularly to replace the water you're sweating out and to prevent thirst from becoming dehydration. A good general guideline is to drink about half a litre (500 ml) of water per hour during moderate hiking in temperate conditions. Adjust this for your own body - the more walks and hikes you do, the more you will learn about what the correct amount of fluid intake is for you.
If it's a very hot day or you're hiking intensively (e.g., uphill with a heavy
backpack),
you may need closer to one litre per hour. Everyone's sweat rate differs, so adjust based on your body - heavier individuals and those who sweat
more will require more.
People vary greatly in their sodium loss, from 200 mg up to 1,800 mg per litre of sweat. One study found that 20% of runners are salty sweaters. You also need to consider how much you sweat overall. If you perspire 'salty' and a lot, you may experience significant electrolyte losses during shorter workouts, making supplements more necessary.14
Again, avoid gulping down large amounts at once. It is better to take frequent small sips to stay hydrated. Many hikers use a hydration bladder or carry a water bottle in an easily accessible spot so they can sip every 10-20 minutes.
Pay attention to your body's signals: drink when you feel even slightly thirsty, rather than pushing on until you're parched. Also, monitor your urine during rest stops - if it's getting dark, make a point to drink more.
Importantly, while you should drink regularly, avoid overdoing it by chugging excessive water beyond what thirst or your sweat rate dictates.
In rare cases, hikers who drank far too much water without enough salt developed hyponatremia (water intoxication).
This is a dangerous condition where blood sodium levels become too low, causing cells (even in the brain) to swell. Symptoms can mimic dehydration (such as fatigue, headache, and nausea), which makes it tricky, but the key is moderation. Do not force yourself to drink beyond thirst in an attempt to stave off dehydration, as this can lead to overhydration.
In a healthy person, thirst is a reliable indicator of need. So, during a hike, find a balance - drink enough to satisfy your thirst and replace sweat, but not so much that you're bloated or needing a wee every 5 minutes. If you notice you're gaining weight from drinking during a long trek, a sign of overhydration, cut back.
Whether it's in water bottles or water bladders, you need to carry hydrating fluids with you.
Hydration doesn't end when the walk is over. Especially after a long or sweaty hike, it is essential to replenish the fluids and electrolytes lost to promote proper recovery. A simple habit is to drink a large glass of water (or a sports drink) as soon as you finish. I like to have a drink as soon as I am back in the car after a walk, along with a small snack, that then tides me over until my next meal.
In fact, exercise science research indicates that for complete rehydration, you should consume approximately 1.2 to 1.5 times the volume of
fluid lost through sweat in the hours following excercise. In one study, athletes who rehydrated with 150% of their sweat loss (for example,
drinking 1.5 litres if 1 litre was lost) performed better in subsequent endurance exercise, improving by about 6-8%.12
You can estimate your sweat loss by weighing yourself before and after your walk. Ideally, do this without clothes, as your post-walk clothes might be heavier due to absorbed sweat. Most of the weight lost is water. Replacing each kilogram lost with approximately 1.5 litres of fluid is recommended.
If you don't have scales, continue to sip fluids regularly until your urine is pale and you are urinating normally again. It's also beneficial to include some electrolytes, carbohydrates, and protein in your post-hike rehydration, as these help your body absorb water more effectively and aid muscle recovery.
You do not need to weigh yourself after every walk, but if you do it periodically and have lost more than about 2% of your body weight, it is a sign that you need to drink more fluids during your walks.
A dependable recovery drink is low-fat milk, which naturally provides the right balance of electrolytes, protein, and carbohydrates for rehydration and can refresh more effectively than water alone. However, any combination of water, sports drinks, and salty snacks can also suffice. If you are health-conscious, note that many sports drinks contain a lot of sugar.
The main point is not to neglect hydration after you stop moving - your body may still sweat and naturally needs water for all the recovery processes (muscle repair, waste removal) following exercise. By ending your day well-hydrated and with a hearty, salty snack or meal, you'll help your body recover and reduce fatigue the next day. Fluid (generally water) and electrolytes, therefore, form part of your essential hiking kit.
Multi-day treks and backpacking adventures pose extra hydration challenges. When you're out for days on end, staying properly hydrated each day is cumulative. If you finish one day dehydrated and don't fully rehydrate, you'll start the next day at a deficit, and over several days, this can seriously affect your performance and well-being. Here are some tips for maintaining hydration on multi-day hikes:
Before setting out, research and identify where you can access water each day, such as streams, lakes, rivers or natural sources. Always carry a filtration or purification method when using natural water sources, such as water filters or purification tablets.
It is wise to top up at every reliable water source along your route, even if you don't feel very thirsty or your water bottles or bladders
aren't empty, because on a multi-day journey, you never know when the next source might be available. Good water management is crucial to avoid
running out between campsites.
Water is heavy - 1 litre weighs 1kg - so you shouldn't carry significantly more than necessary. A common guideline is to take about 2 litres for a half-day of hiking in moderate conditions, or over 4 litres for a full day, depending on heat and personal needs.
Use the sources you plan to refill from and avoid carrying unnecessary weight. So, if you know you pass streams partway around, you can carry less than 4 litres and top up on the way. On very long dry stretches, you may need to carry more. The more walks and hikes you do, the better you will be at gauging your water usage.
A good habit for multi-day hikers is to fully hydrate at your overnight camp, especially if you have a reliable water source. You can also fill up your bottles or bladders for the following day.
Each evening when you reach camp, drink extra water and possibly an electrolyte to replace the day's fluid and salt loss. Similarly, in the
morning, drink a good amount before starting your hike. This way, you begin each day well-hydrated.
Over several days, it's important to monitor hydration levels. Ensure you urinate regularly (at least every few hours) and that the urine is light in colour. If you notice signs of emerging dehydration (such as dark urine, infrequent urination, persistent fatigue, or headache), take action by increasing your fluid and electrolyte intake that day. Learn to recognise your body's signals each day.
If your multi-day trek involves high altitudes or very hot climates, plan to drink more than you normally would. At altitude, the air is dry, and you lose more fluid through breathing, plus thirst can be blunted, so remind yourself to sip regularly even if you're not craving water. Ensure you carry electrolyte replacements in these conditions, not just plain water.
Create a system that makes drinking easy so you're less tempted to skimp. Many backpackers use hydration bladders with a sip hose or keep bottles in shoulder strap pouches, allowing them to drink without stopping. Having the hose next to you is always a reminder to keep sipping. The simpler it is to take a drink, the more consistent you'll be.
That said, many people prefer bottles to hydration bladders. There are pros and cons of bottles or hydration bladders, but you can use both, as I do.
On multi-day ventures, it's vital to replace the salts you continually sweat out. This means using electrolyte tablets or powders in your water, or eating salty snacks daily. A good practice is to have at least one rehydration drink per day that contains sodium. If I'm drinking and sweating a lot, I often take two or three electrolyte tablets, usually Science In Sport (SIS) ones, over the course of a day. This helps maintain your body's electrolyte balance over the long term and can prevent cumulative fatigue and cramping.
When we discuss hydration, it's not just about water. Electrolytes, minerals like sodium, potassium, magnesium, and calcium, are essential companions to water in maintaining your body's optimal function. These electrolytes are lost through sweat. You might notice the salty taste or white salt rings on your clothing after a long, sweaty walk.
If you replace water without electrolytes during extended exercise, you risk diluting your body's salt levels, which can cause problems such as muscle cramps, fatigue, or in severe cases, hyponatremia. Ensuring you consume electrolytes alongside fluids is essential, especially on longer or hotter hikes.
Muscle cramps are the bane of many hikers and often strike when you're dehydrated and low on salts. There has long been debate about the exact cause of exercise-associated muscle cramps; however, studies have observed clear links between hydration and electrolyte status.
For example, a 2004 study found that athletes who experienced muscle cramps during exercise were significantly more dehydrated, having lost more fluids than those who didn't cramp.10
Similarly, research conducted in 2010 revealed that electrolyte imbalances, particularly low sodium, can exacerbate cramping by disrupting normal muscle function. Essentially, when you sweat out a lot of sodium and don't replace it, your muscles are more likely to misfire and contract involuntarily.11
This is why hikers and endurance athletes often consume sports drinks, electrolytes, or salty snacks - it's not just for energy, but to maintain the electrolyte balance that keeps muscles firing correctly. Adequate sodium, potassium, and other electrolytes help your muscles retain the right amount of fluid and prevent the nerve misfires that cause cramps.
It's worth noting that muscle cramps can have multiple causes, such as fatigue and conditioning, but hydration and electrolyte replacement are
among the few factors you can control during your walk to minimise the risk.
I know this from personal experience on several occasions, particularly while participating in mountain marathons. The worst cramps I ever experienced were on a hot summer's day during the Saunders Mountain Marathon at the beginning of July. As I approached the summit of Helvellyn, my leg started to cramp, and we had very little liquid left. I drank what we had, but the continual cramping while trying to jog down the far side to the overnight camp at Thirlmere was one of the most painful days I've ever had in the hills!
So, if you tend to experience calf or hamstring cramps during long walks, pay extra attention to drinking fluids with electrolytes while hiking. Something as simple as a handful of salted nuts, a banana, or an electrolyte tablet in your water can replace what you're losing through sweat and help prevent those painful cramps.
If you experience cramps during a walk, unless you fully hydrate afterwards with electrolytes, you can be sure they will likely return that night in bed. Again, I've personally experienced that on several occasions, and if you are in a small two-man tent, it isn't much fun!
Electrolytes aren't just important for preventing cramps; they are also vital for maintaining your overall energy and avoiding the drained, lethargic feeling that often occurs late in a hike. Sodium, for example, is crucial for regulating fluid balance inside and around your cells. Water containing electrolytes is absorbed more efficiently and stays in your system longer than plain water.
Essentially, your 'water balance' isn't just water - it's water plus the right concentration of salts. By taking in electrolytes, you help your body retain water, maintain blood volume, and keep your nerves and muscles functioning properly. This translates to sustained energy levels and endurance.
You'll also keep your thirst drive stimulated - interestingly, having a bit of salt in your drink or snack makes you naturally want to drink enough water, whereas plain water can sometimes suppress thirst too early.
The best choice depends on personal preference and what you will be happy with. Whether it's through food, electrolyte tablets, drops, or sports drinks, ultimately, they all enter your system and produce similar results once they are dissolved in your intestine.
Where they differ is that if you choose the food route, you need to know that the food you eat provides the necessary electrolytes. If you
opt for electrolyte tablets, drops or powders, these are specifically designed to supply exactly what you need. They also indicate on the
packaging the dosage to use in a specific amount of fluid.
One advantage of the electrolyte route is that, as it is taken mixed in water, it provides both electrolytes and fluids.
There are many electrolytes for sale. The ones I have used for many years now are the Science in Sport (SIS) ones, which have a pleasant taste and agree with my stomach on long walks. It is easy to carry a tube of them in your backpack.
A SIS Berry electrolyte tablet being put into a glass of water
For pre- and post-walk, I have started using Optimal Hydrations OH-E+ Natural Electrolytes, which is essentially ionic fulvic acid. I know the word 'acid' might put some people off, but it is believed to have many health benefits and contains numerous minerals, as well as 72 trace mineral elements.
One ml of Optimal Hydrations OH-E+ Natural Electrolytes is being put into a glass of water
According to them, it is a powerful fulvic acid and trace mineral supplement designed to support energy, hydration, digestion, and recovery. Highly bioavailable and free from additives, it supplies essential minerals your body can absorb fast. I just add one ml of it to my morning and evening glasses of water.
As always, when taking anything, make sure to read the label to check if it is suitable for you.
As I learned from the Runner's World magazine years ago, you can also make a DIY electrolyte drink by adding a small pinch of salt and a splash of fruit juice to your water. Potassium (found in fruits like bananas or in sports drinks) and magnesium (present in nuts, seeds, or electrolyte mixes) also help support muscle function.
As a bonus, consuming electrolytes can more effectively relieve that 'endless thirst' sensation - have you ever noticed how you might drink litres of water and still feel thirsty until you eat something salty? Once you restore electrolytes, the water works more efficiently.
Earlier, we highlighted the danger of overhydrating with water alone. Drinking electrolytes can act as a safety net against this. Hyponatremia, which is a dangerously low sodium level, is rare, but when it occurs, it's often because someone has consumed large amounts of water without salt, thereby diluting their blood sodium. The outcome can be life-threatening (brain swelling, seizures, coma).13
The symptoms may include confusion, headache, vomiting, and, strangely, they can resemble dehydration (which sometimes leads people to drink even more, worsening the condition). It is sometimes experienced by slower marathon runners, who consume a lot of water but little salt.
The good news is that hyponatremia can be prevented by not drinking more than your sweat rate and adding some salt during long exercise sessions. If you follow the 'drink to thirst' approach and have some snacks, you're very unlikely to overhydrate.
Remember: water plus electrolytes equals optimal hydration. Drinking only water in large amounts can cause problems.
Hydration might not be the most glamorous part of walking and hiking, but it's certainly one of the most important for your performance, enjoyment, and safety. By keeping yourself topped up with fluids and electrolytes, you'll maintain higher energy levels, think more clearly, reduce your risk of injury or illness, and recover better for the next walk or hike.
In practical terms, try to make drinking a habit by carrying water where it's easily accessible, sipping frequently, and responding to your body's needs. Plan your water for each hike, especially longer ones, and don't forget to replenish your electrolytes on sweaty days. Your body will thank you with miles of comfortable, cramp-free walking.
Stay hydrated, stay happy, and enjoy your hikes across our stunning UK trails! With the right approach to hydration, you can truly walk on water - or at least with water in your pack or bottle - and feel fantastic doing it.
Happy hiking and cheers (with a big glass of water)!
July 2025
