How To Hydrate Properly For Runs and Races

How To Stay Hydrated When You Run (And Avoid The Porta Potty)

In this episode, I share how to stay properly hydrated during your runs and races and how to calculate how much you should drink to avoid the porta-potty lines. We cover how to calculate sweat and fluid loss, your absorption rate and the importance of electrolytes, specifically sodium and potassium. All this and more coming up on today’s show.

Show Notes

In this episode, I share how to stay properly hydrated during your runs and races and how to calculate how much you should drink to avoid the porta-potty lines. We cover how to calculate sweat and fluid loss, your absorption rate and the importance of electrolytes, specifically sodium and potassium. All this and more coming up on today’s show.

Why Do Runners Become Dehydrated?


Dehydration is a common problem for runners. It can negatively impact endurance and running performance. The reasons for dehydration can be different, it depends on your hydration strategies and personal body requirements.

3 Common Reasons for Dehydration when Running

  1. 1Not satisfying your fluid requirements by carrying little or no drink during the long run which leads to exhaustion and low performance
  2. 2Poor understanding of your sweat rates and fluid absorption rate
  3. 3Drinking concentrated sports drink which may result in stomach upset, nausea or vomiting

Note: Consuming water rapidly and in large quantities may cause Hyperhydration and imbalance of electrolytes like Sodium.

Symptoms of Dehydration

  • Feeling thirsty
  • Fatigue
  • Lethargy
  • Dry eyes and mouth
  • Cramps
  • Muscle spasms
  • GI problems
  • Headache

How To Stay Hydrated When You Run

So a week or so back, I came across a photo of several dogs lined up waiting to pee on a tree and if you saw this photo that I posted in the group,  if you were like me, it made you laugh.  It was this super funny picture in and of itself and for some reason, it instantly reminded me of the porta-potty lines just before, or during a big race that as runners we often have to stand in,   which before the race is OK,  but we often want to avoid them during the race.

And it got me thinking….  Have I covered this before? Have I talked specifically about hydrating properly without having to stop and pee every few miles along your run?

I have talked about the importance of hydration on our performance and the use of water vs sports drinks, in the past, but I don’t think I have discussed it from the point of “How do I calculate the right amount to drink?”.  I may have touched on it, but today, I will try to help you get even closer than just guessing.

Now anywhere there are more than two runners, there will always be a raging debate on how much you should drink,  how often you should drink, what you should drink, what sports drink is best, should you mix and match water and sport drinks or just trial and error a combo of things until you find some combination that works for you.  So while everyone generally agrees that dehydration can hurt your performance, or even contribute to heat illness or worst case, death the debate continues to go on as to how much you really need to drink and at what level dehydration starts to impact you.  Do you just drink to thirst, do you drink a certain amount of ounces per run?So I am going to dig into that today.Frequent stops to the loo, the potty, the bushes, the ally, or under the bridge headed out of Grant park at the Chicago marathon, can impact your performance. Yes, back in 2011 when I ran the Chicago marathon, I saw several people peeing on the sidewalk along the racecourse under the bridge just a few hundred yards past the start of the race. In fact, so many were peeing, that there was this little pee river flowing along the side of the road. Definitely gross since some people were running right through it not realizing what it was.Anyways,  a stop at the porta-potty line during a race can kill your race time.  You can lose 5 minutes or so just waiting if there is a line.  So while it is nice that they are there when you need them,  I hope to give you some tips to reduce that likelihood while making sure you are properly hydrated at the same time.

We All Have a Unique Individual Sweat Rates

When it comes to hydration, a LOT of factors come into play. First and foremost, we all have a unique, individual sweat rate. Some of us are heavy sweaters,  some of us don’t sweat as much and most of us are somewhere in between.

What we consume can impact how much is absorbed and retained by the body.   If we drink caffeinated drinks, like coffee, tea and so on, these are known as diuretics,  because they contain caffeine which in addition to being an energy booster, also stimulates the kidneys to create more urine. And when you create more urine, you are also flushing valuable sodium,  an important electrolyte from your body.  Now if you consume a lot of sodium in your diet,  flushing excess sodium out can be beneficial, especially if you have higher blood pressure because it does help reduce more of the water, in the blood which then lowers the pressure buildup on your blood vessel walls,  but for most of us, getting rid of fluid volume in our blood and reducing sodium levels during athletic events like running is something we want to avoid.  A little energy boost of coffee won’t hurt you and can help you with a boost of energy,  but you don’t want to be hydrating on ice tea and coffee all week either,  which in the Summer, I tend to do because I like drinking ice tea and it helps me avoid the more destructive sodas which I rarely drink anymore, because of better alternatives like water and tea.

So when it comes to fluid retention, a couple of other things you should be aware of if you aren’t already.


Sodium, which most of us consume plenty of,  helps us hold on, or retain fluid.

Potassium and other electrolytes also come into play.

Depending on how far you run or how long you will be out on a run,  this may be an important contributor to how much you need to consume and how often. So, before we get to the calculation section, I want to take a few minutes to talk about electrolytes and their role and why it can be so damn hard to figure out what is right for you.  Having this level of understanding will help keep you hydrated properly without overdoing it.

According to the Coaching Association of Canada, and a few other places I checked, the recommended daily intake of sodium for adults is 1500 mg with a suggested upper limit of 2300 mg. The average sodium intake of most adults though is actually estimated to be around 3400 mg per day.  So way over what we are supposed to consume. This is mainly due to the fact that sodium is in just about everything we eat, especially in processed foods.  In fact, many can go over this amount in just one meal.  And, because of this, chronic overconsumption of sodium can lead to health concerns, such as hypertension (high blood pressure), stroke, heart disease and/or kidney problems.

Sodium Needs For Runners


Consider this:

  • Runners sweat between 400-2400 mL which is 13-80 ounces per hour of exercise which is a wide range, BUT the average is around 1200 mL per hour, which is about 40 ounces per hour.
  • In addition to water, the main electrolyte lost in sweat and urine is sodium.
  • The sodium content of sweat varies substantially from 115mg to greater than 2000 mg per 1000 mL of sweat which is about 33 ounces.
  • So,  a runner  who is a “salty sweater” (i.e., who has a high amount of sodium in their sweat) may lose well in excess of the recommended intakes in just over an hour or so of running.  If you sweat a lot and notice the salty residue on your skin as the sweat dries, that is the sodium or salt, that you just lost.

Symptoms of Sodium Deficiency

  • Muscle cramps
  • Fatigue
  • Dizziness
  • Nausea
  • Inability to concentrate

 Ever have brain fog late in the race,  maybe confusion?  It could be caused by low sodium levels, but also by low glycogen (or sugar levels).

What to Do if You’re a “Salty Sweater”

  • Enrich your diet with salty foods such as broth, pickles, salted nuts, olives, V-8 juice, etc.
  • Hydrate yourself with a sports drink that contains Sodium during the run.
  • If you take part in long-distance events such as ultra-marathons or triathlons, try to consume 100-250 milligrams/8 oz. of water during racing.

Potassium Needs For Runners


Potassium is the primary electrolyte located inside the body’s cells and is stored in muscle fibers along with glycogen. For those not familiar with glycogen, is is carbohydrates you ate, that has been converted and stored as sugars in your muscles cells / and liver that your body can quickly tap into when it needs to do something.  Your body fat is another form of stored energy.  Glycogen just converts quicker so it is usually the primary source of energy and is then supplemented by body fat whenever your body needs it.

  • Potassium plays a critical role in converting your stored energy into actual action, by helping transport glucose into the muscle cell to be used. 
  • Potassium also interacts with both sodium and chloride in order to help control fluid levels and electrolyte balance in your body.  This is important as both sodium and Potassium help regulate the amount of fluid retention in your body.  What isn’t retained is flushed out when you go to the bathroom.  And while not important for today’s discussion, Potassium assists in the conduction of nerve impulses that fire/trigger your muscles to move.

So as we run, muscle cells get depleted of potassium as part of this energy conversion. As a result, there is a greater concentration of potassium getting released back into your blood and since blood is where your sweat comes from, lost through sweating. So we lose potassium through sweat and urine loss.

So how much Potassium do we lose?  Generally speaking, about 100-200mg/hour.

If our runs are longer than an hour, hour and a half, we want to look for ways to replace about 75-150 mg/hr. So while we lose 100-200mg as an average adult, if replaced all at once, it can actually throw off your sodium balance as well (since the two work together and your body will work very hard to keep those in sync harmoniously),  not to mention, too much potassium is hard on your stomach and can lead to severe stomach distress.

Symptoms of Potassium Deficiency

  • Nausea
  • Slower reflexes
  • Vomiting
  • Rapid heart rate
  • Muscle weakness
  • Muscle spasms
  • Cramping

So for those of you who are running more than 90 minutes or so, electrolytes should be replaced either via sports drinks or GU’s/Gels, or any chew/gel that contains electrolytes.  Generally speaking, these also contain carbohydrates which also need to be replaced around this time. And,  if running LESS than 90 minutes, most don’t need to do anything.

Last update on 2024-05-11 / Images from Amazon Product Advertising API

Last update on 2024-05-11 / Images from Amazon Product Advertising API

Last update on 2024-05-10 / Images from Amazon Product Advertising API

And this is the reason, that many people complain about GU’s/Gels causing stomach distress.  They either consumed too many,  or they are dehydrated or some combination of both that leads to the stomach distress and nauseous feeling NOT the Gu or Gel itself.   If you take them properly and are hydrated at the right level, you will be a lot less likely to experience side effects.   The problem is, most of us don’t take them properly.  If you read the package on a gel, it will give you general instructions, which is a great starting point, but then if you’re not taking in enough fluids, specifically water, you are concentrating the amount of potassium in your blood.  So you need to use them in addition to taking the proper amount of water to keep it diluted enough to get get the side effects, but strong enough to get the benefit,  and this takes practice.

So the thing we can take away from all of this is that the needs of runners are different between each individual runner in both terms of sweat rate and electrolyte loss. And, what we drink can impact the speed/levels of electrolyte and fluid loss in terms of fluid loss through urinating and sweating. And, the length of the run. All of these have an impact on how much we need to be drinking, what we should be drinking and how much electrolytes we should be taking inSo with that background, now we can talk about how much should I drink, or not drink to avoid having to pee every few miles…..

10 Best Sources of Potassium to Add to Your Diet

  • Sweet potatoes
  • Beans
  • Bananas
  • Dried apricots
  • Kale
  • Avocado
  • Spinach
  • Broccoli
  • Beets
  • Coconut Water

How to Calculate How Much You Should Drink

So we talked about runners losing as much as 13-80 ounces of sweat per hour of exercise with the average being around 1200mL or 40 ounces per hour.  To put that in perspective, the average hand-carry water bottle that many runners use comes in around 16-20 ounces.  The average Gatorade or water cup in a race is about 5-8 ounces depending on the size of the cup they use and how far they fill it up.  So if the average runner consumes 5 ounces every mile and averages 6 miles during that hour,  then they have consumed about 30 ounces per hour, while losing on average 40.  I’ll let you do the math based on how fast you run and whether or not you are getting 5 ounces per stop, or IF they even have a stop every mile. Many races put out hydration stops every 2 miles.

The highest recorded sweat rate for an athlete in an exercise situation is 3.7 liters (125 oz.) per hour, recorded by Alberto Salazar while preparing for the 1984 Summer Olympics. The highest human sweat rate recorded ever is 5 liters (169 oz.) per hour and was measured on a resting body exposed to a very hot environment. They weren’t even exercising. At rest, the blood flow to this person’s skin was at maximum and not competing with exercising muscles. By the way, your blood diverts to your skin in warm weather to help facilitate sweating.  This blood volume is taken away from muscles which is why it is so damn hard to run in higher temperatures…. Ok, so what is your starting point for hydrating and how do we figure out what is right for you?

Well, first we start, with making sure you are hydrating properly.  Even though we want to avoid the porta-potty line, we have to first make sure, we are staying hydrated first and foremost.

  • Now, you may have heard about the “weigh yourself naked before and after a run test”,  and that certainly is one way to estimate how much you sweat and we will use this as well.   The idea is that if you weigh yourself naked before a run, and then naked after a run,  that will tell you how many pounds and/or ounces you lost during your run.  So if you calculate the appropriate ounces per hour you lost, then that is how much you need to consume to stay properly hydrated. If you did not use the toilet or consume any fluids during exercise, your weight loss is your sweat rate. For each kilogram of lost weight, you lost one liter of fluid. For each pound lost, you lost 15.4 oz. of fluids.  If you did use the restroom or drink water or a sports drink then you have to account for that.

But here is the problem.

Your result changes based on a whole lot of factors!  Temperature and humidity, for starters,  play into how much can evaporate and how much you sweat and we also talked about consuming diuretics like caffeinated drinks, even alcohol, or use of lack of electrolytes, can impact how fast fluids go through you to your bladder. But did you know stress, pace, fitness level, body size, specific surface area, gender all have an impact on your sweat rate?  So,  really the only way to combat this is to test yourself under a variety of factors.So while this is a good exercise to get you started,  it is only an estimation.  In cooler temperatures, you won’t sweat as much, but you will still lose some through breathing and some sweating.  But if you calculated your fluid levels based on warm temperatures, if you take on that much fluids on a cooler day, you may end up needing to go to the bathroom.

  • So get yourself a log,  and periodically test your sweat/fluid loss rate under varying conditions. Log the temperature and humidity each day you do the test.  I recommend using some form of workout log anyways, but if you use a paper-based notebook for a log, keep these numbers on a separate page dedicated to logging these over time.  Look for similarities where temperature and humidity levels were close to each other and look at the averages to see where you fall.  You don’t need to do it a lot, but it will get you closer than just randomly doing it, or doing it once and just keeping those numbers.

This will get you a lot closer, but there is one other problem that you need to be aware of.

Fluid Absorption Rate in Runners

So if sweat rate is what we ‘lose’,  then what we take in has to be absorbed and used right? And that is where another problem can creep up…

  • Average fluid absorption rates in runners range from 0.8 to 1.2 liters per hour (27.4 to 40.6 oz.).

And, while the sweat-rate and fluid-absorption ranges are close for many people, some runners sweat at higher rates per hour than their fluid-absorption rate. So,  they can’t absorb the fluid as fast as they lose it,  so in short races, this rate discrepancy isn’t so much of a problem; however, for longer races, this rate difference can lead to dehydration and decreased performance or if they consume too much that they can absorb, then nausea and vomiting can occur they attempt to consume more fluids and fuel than their bodies can handle. So even if you manage to hold down the extra fluids, it can lead to extra weight or fluids sloshing around in your stomach…. Ever run and feel water or Gatorade sloshing around?  Fluid absorption.So I would first approach this from the perspective of fluid loss, since that is the easiest to test, and start there, by trying to backward calculate how much you need to replace… Then if you find yourself struggling with absorption (and you tried spreading the intake of fluids out to maximize what you can handle,  then back down.  If you find yourself, having to stop and use the restroom,  back down slightly.  The longer the race, the more I would error on consuming more, than trying to avoid the porta-potty,  and if you feel the urge, maybe skip one stop and resume with the next as often the feeling goes away, but for longer races, dehydration can impact you far beyond a porta-potty stop,  but for shorter races, especially cooler races, error slightly towards under consuming (not by much) but consider dialing it back in order to avoid the porta-potty line.

It certainly isn’t 100% but with testing and practice (and it takes discipline to actually do it) you can figure it out for yourself so it isn’t so much guesswork.   Obviously emptying your bladder before a race, gives you some additional wiggle room,  but don’t hold back drinking some water pre-race as it is beneficial and worthwhile t start the race well hydrated, and most will be converted to sweat anyways.

Key Takeaways

  • Ensure 30-45 minutes before the run to drink at least 8 fl. oz.
  • Try sipping water every 15-20 minutes about 5–10 fl. oz. to prevent dehydration but not to overflow yourself
  • Consider preparing an electrolyte replacement sports drink for the long run.
  • Weigh yourself before and after a run to determine your sweat rate. It will help you replace the fluid lost in sweat during the long run.
  • Take into consideration your absorption rate. Don’t drink loads of water before the run and don’t try to replace very lost liter, it will just make you searching for a toilet or cause Hyperhydration.
  • Prevent electrolyte imbalance by proper daily hydration and diet rich in sodium, potassium and other electrolytes like magnesium and calcium that can also benefit your health and performance.

I hope you found this helpful and be sure to check out the full episode by subscribing and listening to the podcast.Thanks and Happy Running!