How Much Water Do Runners Need?
- Adequate hydration optimizes your health
- You should adequately hydrate the day before you exercise
- There is no single water consumption recommendation
- Learn to judge if you are hydrated by checking biomarkers
- Drink water slowly throughout the day
- Only drink water as you are thirsty during exercise
Common knowledge says it’s important to exercise hydrated. We sweat to regulate our body temperature, and that requires water. How much water do we need? I reviewed the academic research on hydration and the short answer is, it depends. Before we go into how much water we need and when to drink, let’s take a step back and talk water.
All living things need water. Straight up. It is the most important nutrient and the only one that we would die within days without1.
You should stay adequately hydrated every day, not just on days you run.
Besides needing water to survive, getting the right amount, as in being adequately hydrated on a regular basis, is really good for you. So many aspects of your health depend on hydration. Research shows that hydration influences the following:
- Cognitive ability2
- Physical performance3
- Mood4
- Gastrointestinal function5
- Exercise induced asthma6
- Kidney stones7
- Headaches and migraines8
- Healthy skin9
Our bodies will perform their best in everyday life, including exercise, when we are hydrated. You should stay adequately hydrated every day, not just on days you run. Adequate hydration the day prior to exercise is part of the American College of Sports Medicine recommendations.10 If you find a routine that works, and develop the habits to be hydrated on the daily, you’ll always be ready to exercise. Although exercising does change your hydration requirements. We'll cover exercise based recommendations shortly.
Are you hydrated enough, day to day? If you are chronically dehydrated your body is likely not running at 100%. If that's the case, this is a major opportunity to easily improve your well-being. Hydration is the "low hanging fruit" of fitness / health considerations. This isn't as demanding as 100 pushups, an hour of meditation, or fasting. It's just drinking water, slowly and regularly, as part of your lifestyle.
Besides, if you make adequate hydration a part of your lifestyle, that’s one last thing you need to worry about when preparing to exercise.
So let's do it. Finish reading the post and start to get hydrated on the daily. Don’t put yourself at risk of a headache, crabbiness, forgetfulness, and/or constipation! Besides, if you make adequate hydration a part of your lifestyle, that’s one last thing you need to worry about when preparing to exercise.
How much water do we really need?
There is a myth that everyone needs 8 glasses of water a day11.
Nonsense, how could 8 cups of water be the exact amount for everyone? How much water each person needs depends on activity level, diet, age, body composition, attire, climate… it’s complicated. The current US Dietary Guidelines don’t even have a recommendation because it’s impossible to prescribe a standard amount12.
You are going to have to figure out much water you need. To do that you need to know when you are hydrated or not.
Knowing if you are hydrated seems like an easy thing, right? Nope. There is no scientific consensus on the best method to assess hydration status, outside of a laboratory13.
There are three biomarkers to assess hydration levels without lab tests: urine color, thirst, and body mass. They are not perfect, so you’ll have to combine a couple to get a sense of how much water you need, day to day14.
The time to check your urine color is first thing in the morning (assuming an overnight fast)15. Consider it a score on how you did the previous day and review how much you drank versus activity level.
Urine color
OK, we’re going to go there. Time to be mature, Mac, and stay away from potty humor. How about this: you can write pee rather than urine a few times, sound good? You can do it. Here we go.
Checking the color of your urine is a commonly suggested method for accessing hydration. Lighter means more hydrated and darker means less. It’s very important when you check the color. The time to check your urine color is first thing in the morning (assuming an overnight fast)15. Consider it a score on how you did the previous day and review how much you drank versus activity level.
| Urine Color | Hydration Level |
|---|---|
| 1 | |
| 2 | |
| 3 | |
| 4 | |
| 5 | |
| 6 | |
| 7 | |
| 8 |
Throughout the day its color might not accurately show your hydration level. If you are drinking large amounts of water in a short span of time, it’s going to be more clear, even if you are dehydrated16. This is because your body can only absorb water so fast, and your pee is clear because of extra water your body isn't using. If it's in regions 4 or higher, you are dehydrated.
You'll have to combine pee color observations with another indicator to accurately know your hydration level.
Waiting until you are thirsty to drink won’t keep you consistently hydrated17.
Thirst
Thirst is a simple biomaker of hydration. Thirst is one of our body's physiological responses to dehydration. It's certainly more natural than looking at your urine color! The drawback is you start to feel thirsty after you are dehydrated, which you want to avoid. Waiting until you are thirsty to drink won’t keep you consistently hydrated17. If you don’t ever feel thirsty, you are probably doing something right. If you don't ever feel thirsty AND your pee color is in the good zone the next morning then you were right on.
Body mass
Body mass is another non-lab based measure of hydration level. Your weight fluctuates throughout the day based on how hydrated you are. You are dehydrated when you lose about 1 to 2% of your body mass. If you are weary of possible harmful psychological affects of monitoring weight on a daily basis, I understand your concern. A meta-analysis of twenty articles by Packanowski, et. al. 2015 suggests that daily weighing creates a risk of adverse effects in some people18.
Personally I just look at the my pee color and consider my thirst and I am not interested in tracking my weight. However, body mass is a valid biomarker, and is particularly helpful to assess how much water you need to drink after exercise. Remember, it alone is not accurate enough, and you need to also consider thirst and/or urine color.
Use multiple biomarkers
As I have mentioned throughout this article, you should use a combination of the three indicators to judge your hydration level. Thirst and urine color are biomarkers that work for me. Keep track of how much water you drink and figure out how much you need to be adequately hydrated. This can be as casual or formal as fits your personality. I am not interested in logging how much water I drink, but I understand that would work well for some. The other variables you need to consider day to day are your activity level, diet, attire, and sweat production.
You can drink too much water
Dilutional hyponatremia is a dangerous condition when the level of sodium in the body is too low because the body has too much water19. It is sometimes called water intoxication as the symptoms are similar to other forms of intoxication: fatigue, nausea, vomiting, headaches, blurred vision, confusion, restlessness, irritability, and lethargy. In severe cases it leads to coma and can be fatal. While it is relatively rare, studies have found that 10 - 20% of sampled marathon finishers have cases of hyponatremia20. The studies indicated the marathoners drank too much water during their races.
So figure out how much water you need and don't over do it, especially if you don't sweat much during exercise. We will cover recommended practices during exercise next, but one is to only drink water as you thirsty, during exercise. Know the signs of hypnotremia, and if you establish a new routine check in with your local health care professional.
Exercise specific considerations
The American College of Sports Medicine has very clear evidence based recommendations for water consumption and fluid replacement10. They reference many of the same scholarly works as this article and agree on the need to customize hydration plans and using a combination of biomarkers to assess hydration status. I will summarize their recommendations then discuss afterwards.
- Proper hydration is essential for performance, and safety
- Too little body water increases risk of heat illness
- Too much body water is dangerous too, especially in women and older individuals
- Try to properly hydrated through regular routine and diet
- At least 4 hours prior, slowly drink (about 5-7 mL per kg or 4 oz per 50 lbs) beverages
- If urine is highly concentrated (dark), extra hydration is needed, slowly drink additional beverages (about 3-5 mL per kg or 2.5 oz per 50 lbs) about 2 hours prior to exercise
- Ideally you should not need to urinate extra amounts before exercise
- During exercise periodically drink water as you are thirsty, between 0.4 L and 0.8 L an hour, especially when rapidly sweating, or when exercising for prolonged periods
- Goal is to avoid losing more than 2% of your weight to sweat
- After exercise, slowly replace fluids lost to sweating, depending on how much body weight lost (1.5 L per kg)
If you want to really dig deep into this topic check out the full paper.
This study provides recommendations for everyone, including competitive athletes. Certainly a college athlete is placing much greater demands on their body than me, and I assume most of my readers. And the requirements among physical activities vary greatly. Consider how much more a football player will sweat in their pads and jersey compared to lightly dress runner.
The big takeaways, for the non-competitive runner, are:
- be properly hydrated before you run,
- don't drink water too fast, before, during, or after exercise,
- the more you sweat, e.g. by exercising in hot temperatures, the more water you need
- don't over do water consumption and risk dilutional hyponatremia,
- it's essential to accurately access your hydration level
What about sports beverages?
This is a bigger topic than I want to cover in this post, but one that I want to explore. Here are the basics, sports drink contain sugar and electrolytes (sodium and potassium). When you sweat you lose electrolytes, and your body's state of hydration is affected by both your total body water and sodium levels. Do you need a drink with electrolytes replenish your body? Not really. Regular meal consumption covers electrolyte replacement for most individuals 21. You should eat nutritious food after you exercise. If eating isn't an option then consuming sports drinks will help replace necessary electrolytes 22. Replacing lost electrolytes is not as important if you don't sweat very much because of your sweat rate and/or the duration of your exercise.
About coffee
One last thing. I've heard countless times that coffee is dehydrating. And many times when I've told people my favorite drink after a run is a great cup of coffee, I've heard surprise that I would follow up a healthy activity with an "unhealthy drink". Listen up, if you are going to come at coffee like that, you need to come correct! Let's clear this up: coffee is hydrating23. In fact, 40 studies, with over 3.5 million subjects found moderate coffee consumption (2-4 cups) reduced mortality from all causes including cardiovascular disease and cancer24. So, don't let anyone slander coffee and suggest that it's dehydrating or bad for you.
Regular exercise is the most effective self-care possible. Your body will feel better and perform better when you are hydrated. Insuring you feel good when you run is essential to the Running Kindness goal: wanting to go on another run. Learn how to access your hydration level and drink water slowly and regularly throughout the day. If you find running and your running program difficult, follow the Running Kindness plan. Life is hard, exercise doesn't have to be. Much love to everyone.
3. Murray B. Hydration and physical performance. J Am Coll Nutr. 2007;26:542S–548S.