Hydration for Runners
You cannot ignore hydration if you want to run well. Your body needs water to function, especially under the stress of running. Every cell, muscle and joint depends on fluid balance. Dehydration can hit your performance before you even realize it is happening. If you have suffered from dehydration in the past you can attest to this.
Drinking water is not something you do just before a race and at the finish line. If you are serious about running, you need to think about hydration on a daily basis.
The Importance of Hydration for Runners
Your body is made up of over 60% water. When you run, you sweat. That’s your body’s way of cooling itself down. The more you sweat, the more fluid your body is losing.
Water helps regulate your temperature, lubricate your joints, carry nutrients, and remove waste. Without it, your energy drops, your muscles tighten, and your risk of heat exhaustion or cramps increases.
Even a small dip in hydration, 1 to 2% of body weight lost through sweat, can reduce your running performance. You may feel slower, sluggish, or dizzy. Your focus suffers and your recovery takes longer.
How Much Water Should you Drink Every Day?
The U.S National Academies of Sciences Engineering and Medicine have determined that an adequate daily fluid intake for men is, 15.5 cups(3.7 litres) and 11.5 Cups(2.7 litres) for women. That seems like a lot of water for one person, but remember that we do get water from food also.
Keeping within the 2 to 3 litres range is an ideal baseline.
Several factors can significantly increase or decrease your fluid requirements:
Body Size and Composition
Larger people will need more water than smaller individuals. If you have a higher muscle mass your hydration needs will also increase.
Activity Level
The more active you are, the higher your baseline requirement for water. A construction worker will require more hydration than an office based worker. Throw in running, walking, weight lifting or other forms of exercise and this increases further.
Environment and Climate
Hot weather will increase your sweat rate. Your body will be working hard to regulate it’s core temperature and this will result in fluid loss.
Colder weather can also be deceptive, as dry air increases water loss through respiration and heavy winter gear can make you sweat.
High altitudes increase respiration due to lower oxygen concentration. Loss of water is also caused as a result of a more frequent urge for urination as the body tries to regulate it’s pH levels.
Long Haul Flights, due to the altitude factor can also cause varying degrees of dehydration. It is important to consume water to alleviate this risk. Runners enjoy travelling to races in other locations and this may involve a long flight. Ensure you are topping up with water during and after the flight to avoid any issues on race day.
Sweat Rate
You may have noticed how some runners sweat more than others. Our sweat rate is affected by genetics, fitness level, and acclimation to heat.
What we wear will impact the sweat rate. Overdressing for a run can lead to a very uncomfortable session. Layering is best in cooler conditions as you can remove as necessary. In hot conditions, exposed skin will cool faster but be sure to wear sunscreen.
Diet
Coffee and Tea are diuretics which cause an increase in urination. If you eat a lot of salty or processed foods your body will need extra hydration to flush out the excess sodium.
Illness, Injury or Stress
Illness involving high fevers, diarrhoea or vomiting will cause the body to become dehydrated. Inflammation and stress can increase fluid loss.
Hydration Starts Before the Run
The best strategy for hydrating for running is to drink water every day. Increasing your intake a day or two before a race or long run is better than trying to chug down 2 litres of water before you head out the door. This can lead to bloating, and possibly the need for a toilet break mid-run. Having a tummy full of water sloshing around is not conducive to a pleasant running experience.
A good habit is to start your day with a large glass of water, then sip continuously throughout the day. To avoid too many bathroom trips during the night, avoid drinking water late in the evening.
Should I Drink Water During a Run?
Should I drink water during a run? That depends on the distance, the weather, and your sweat rate.
For a 5K, most runners don’t need to drink unless it’s hot and humid.
In a 10K, some sips midway may help if you’re running for over an hour or sweating heavily.
For a half marathon, hydration becomes more important. Drinking small amounts every 20–30 minutes can help keep energy up and delay fatigue.
Running a full marathon? You need a solid hydration strategy. Drink early and often, waiting until you feel thirsty is too late. Your marathon hydration strategy is something you need to practice during your long training runs.
For more advice on marathon hydration strategies, check out: Marathon Training Strategies
How Much Water Should You Drink During a Run
To know how much to drink during your runs, you need to know your sweat rate. That’s where the sweat test comes in.
Weigh yourself, without clothes, before a run. Run for 30 minutes or 60 minutes, depending on your level. Weigh yourself after your run, again without clothes.
Every 1 gram of body weight lost equals 1 ml of sweat. If you lose 1000 grams (1 kilogram), that’s 1 liter of fluid lost. (If you ran for 30 minutes, multiply this number by 2 to get your hourly sweat rate)
Use that number to guide how much to drink per hour of running. You won’t replace every drop during the run, but you’ll get close enough to maintain performance and avoid dehydration.
How Much Water Should you Drink After a Run
How much water should I drink after a run? Your goal is to replace lost fluids within 1 to 2 hours of finishing.
Use your sweat test results. If you lost 500ml, aim to drink 500–750ml after your run. Don’t just sip and guess, be intentional.
Combine your water with some electrolytes or salty food to help absorption and rebalance what you lost through sweat. Again, check your urine colour. This should be a pale yellow(2), if it is a dark yellow/orange colour (4 or higher), you need to take on water. That’s your easiest feedback tool.
Urine Colour Chart
Signs That You Are Dehydrated
Dehydration can creep up without warning. Here’s what to watch for:
- Dry mouth or throat
- Dizziness or light-headedness
- Headaches
- Dark yellow urine
- Muscle cramps
- Sluggish pace or early fatigue
- High perceived effort
If you’re feeling these on your run, you’re likely underhydrated. Stop, hydrate, and adjust next time.
Should I Take Electrolyes for my Run
Electrolytes are minerals that carry an electric charge. Your body needs them to survive, especially when you’re active. The main electrolytes lost in sweat are sodium, potassium, magnesium, and calcium. These minerals help control muscle function, nerve signall
ing, hydration, and pH balance.
When you sweat, you don’t just lose water, you lose electrolytes too. That’s why drinking plain water isn’t always enough. If you run long, train in hot weather, or sweat heavily, you risk depleting these key minerals. And when electrolytes fall too low, performance suffers.
Sodium, (salt), is the most important electrolyte for runners. It helps your body retain fluid and maintain blood pressure. When sodium drops too low, you may feel weak, nauseous, or light-headed. In extreme cases, you can develop hyponatremia, a dangerous condition where your blood becomes too diluted.
Potassium helps regulate heartbeat and muscle contractions. If you’ve ever had post-run muscle cramps, low potassium might be part of the cause.
Magnesium supports muscle relaxation and energy production. Too little can lead to twitching, fatigue, and cramping.
Calcium is often thought of in relation to bones, but it also helps with muscle contractions and nerve signaling.
You don’t need to obsess over numbers, but you should know this: the longer and sweatier your run, the more electrolytes you need to replace. If you’re only running 30 minutes, water may be fine. If you’re out for over an hour, especially in heat, add electrolytes.
You can get them through sports drinks, tablets, powders, or electrolyte chews. Some brands include carbs for energy, while others are sugar-free. Test a few and find what works best for your stomach.
Don’t wait for signs of imbalance. By the time you’re cramping or light-headed, it’s already too late. If you’re unsure, start with sodium, it’s the most critical electrolyte to replace during long runs.
How to Carry Water When Running
What is the best way to carry water on a run? Many runners don’t enjoy carrying anything while running, especially water. There’s no one answer, but there are plenty of options:
- Handheld bottles
- Hydration belts
- Hydration vests
You can also stash water bottles along your route if you’re doing loops. Drive out early and place them safely. Or if your route takes you by a convenience store, pop some money or bank card in your pocket and stop in for a bottle of water or sport’s drink.
Running with water takes planning, but it’s far better than hitting the wall mid-run because you didn’t prepare.
Hydration for Runners: Final Thoughts
The key to knowing how much water to drink before, during or after a run is having a good understanding of how your body responds to factors like heat, effort and duration. Do not rely on guesswork. You can track your weight before and after a run, do the pee test and keep track of your water intake.
It may be useful to ask yourself the following questions:
- How much water do I drink every day?
- How do I feel on runs when I don’t hydrate well?
- Do I know my sweat rate?
- Have I practiced drinking on long runs, did I hit a wall at any point?
- Do I use electrolytes when I need them?
- Have I suffered muscle cramps, what were the conditions?
Keeping a running journal can help pinpoint where your hydration is working and where you need to make improvements.
Proper hydration can be the key to help you perform better, recover faster, avoid injuries, and make your runs more comfortable.
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