For years, a glass of water before lacing up felt like due diligence. A ritual, almost. The problem is that drinking plain water immediately before a summer run, and only then, is one of the most common, and quietly counterproductive, things runners do. A marathon coach will tell you this within the first five minutes of discussing your training. The mistake isn’t that you’re drinking water. The mistake is how and when you’re doing it.
Key takeaways
- The timing of your hydration matters more than you think—a glass of water 5 minutes before your run doesn’t give your body time to absorb it
- Plain water alone during summer heat can be dangerously counterproductive, potentially leading to a serious condition even experienced runners overlook
- One unexpected indicator of overhydration reveals itself in the color of your urine—and it’s the opposite of what most runners believe
The real problem with “drink before you run”
Simply drinking more water isn’t always the full solution when temperatures rise. The instinct to down a large glass of water right before heading out the door is understandable, but it treats hydration as an event rather than a process. If your plan is to chug a bunch of water right before your run, think again. Hydrating properly actually requires focusing on your fluid intake well before the run ever begins. That means hours, not minutes.
Relying solely on thirst as a guide frequently leads to underhydration by nearly 50%, so fluids should be consumed before, during, and after exposure to heat. The body doesn’t absorb a half-litre of water in the ten minutes you spend stretching by the front door. If you focus on drinking water and staying hydrated throughout the day, you won’t need to worry about it quite as much right before your run or even during it. The pre-run glass of water feels productive; the sustained, day-long approach is what actually works.
There’s also a timing issue specific to summer running. As you sweat more in the heat, your body loses fluids and electrolytes at a faster rate. Even mild Dehydration can cause your pace to slow down and trigger an upset stomach, because blood is redirected away from your stomach to help cool your skin, making it harder to digest fuel or fluids mid-run. Gulping water right before you set off can make this worse, not better.
The one thing the coach actually changed
The real revelation isn’t about drinking more. It’s about what you’re drinking and what you’re leaving out. When the temperature rises, your sweat rate increases, which means you’re also losing sodium, potassium, and magnesium. Water alone won’t replace those electrolytes. This is the fundamental gap in the “glass of water before every run” ritual. Plain water dilutes what’s already circulating in your bloodstream without replenishing what summer heat is stripping away.
When you sweat, you lose not just water but electrolytes, mostly sodium, but also potassium, magnesium, and chloride. For long runs over 60 minutes or very sweaty workouts, water alone isn’t enough. A marathon coach’s correction, then, isn’t dramatic — no ice baths, no exotic supplements. Pre-hydrate with 16–20 oz of fluid (or an electrolyte drink) 60–90 minutes before your run, rather than five minutes beforehand with plain water. That window gives your body time to actually absorb the fluid and hold onto it during the effort ahead.
Adding sodium to your pre-run drinks helps you absorb and retain more fluid in your bloodstream. Just drinking water when sweating over long periods dilutes your sodium levels, which can impact Your Performance and could lead to hyponatremia. That word, hyponatremia, sounds clinical and remote, but it’s a genuine risk for summer runners who are well-intentioned but poorly informed about electrolytes.
Hyponatremia: the hidden hazard of drinking “too well”
Exercise-associated hyponatremia is a fluid-electrolyte disorder caused by a decrease in sodium levels during or up to 24 hours after prolonged physical activity. It can develop when runners drink more fluid than their kidneys can excrete, severely diluting the sodium in the blood needed for organs, especially the brain, to function properly. This sounds like a condition reserved for ultramarathon runners, but it isn’t. Athletes who drink too much before and during prolonged exercise in warm, humid climates are at risk of developing hyponatremia. Small, slow athletes who sweat a lot, excrete a salty sweat, and are overzealous in their drinking habits are theoretically at greater risk.
Common symptoms of hyponatremia include nausea, vomiting, headache, confusion, fatigue, and muscle cramps, and because these overlap with dehydration symptoms, the condition can be challenging to recognise. Many runners who feel terrible in the second half of a summer long run assume they haven’t drunk enough. Sometimes, they’ve drunk too much of the wrong thing. Runners can avoid hyponatremia by balancing water intake with electrolytes, especially sodium — ensuring proper hydration without diluting the essential minerals the body needs to function well.
Building a smarter summer hydration habit
The practical shift is simpler than most runners expect. Drink steadily throughout the day and balance your water intake with electrolytes by incorporating sports drinks or electrolyte supplements into your hydration plan, especially during long runs. A useful daily check: pale yellow urine is a good sign you’re hydrated. Colourless urine, counterintuitively, can indicate you’ve drunk too much plain water and flushed out too many minerals.
The simplest way to find out how much fluid you lose? Weigh yourself (without clothes) before and after your run. Every kilogram you lose roughly equals one litre of fluid you need to replace. This sweat-test approach sounds fiddly but takes about thirty seconds and genuinely personalises your hydration strategy, because sweating is related to genetic factors, diet, body weight, heat acclimatisation and other physiological traits, leading to a wide variation in the amount of sweating and sodium loss across individuals.
During runs longer than 45 to 60 minutes, sipping a carb-electrolyte mix every 15 to 20 minutes helps stay ahead of dehydration and keeps energy steady. And after? Rehydrate with water or an electrolyte drink to replenish fluids and electrolytes lost during exercise, aiming for around 480–720 ml depending on how much you sweat.
One detail worth knowing: it can take between five and seven days of active exposure in hot conditions to properly acclimatise the body to extreme temperatures. During those early summer sessions, your body is losing significantly more sodium than it will once it’s adapted. That’s the week you’ll feel worst on your usual route, and the week when plain water is least adequate of all. Adjusting your electrolyte intake at the start of the season, not just when you feel awful mid-run, is the change that makes the biggest difference.
Please consult your GP or a registered sports dietitian for personalised hydration advice, particularly if you have any underlying health conditions.
Sources : precisionhydration.com | illinoismarathon.com