If you've ever finished a run feeling like a wrung-out towel, or worse, cramping up around mile 5, then hydration is probably part of the problem. The advice out there is all over the place. Drink 8 glasses a day. Drink when you're thirsty. Drink a gallon before you head out the door. None of that is specific enough to actually help you perform better.
How much water you need is much more specific to the individual than all these blanket strategies. It depends on your body weight, the weather, and, how much you sweat, and how long you're out there. There's no single number that works for everyone. But there is a framework, and once you understand it, you'll stop guessing.
Before Your Run
Your goal here is to start hydrated, not to chug water 10 minutes before you head out.
The night before: Drink normally with meals. If you've got a long run on the calendar, add an extra glass with dinner.
2-3 hours before: 16-20 oz of water. This gives your body time to actually absorb it instead of just passing through.
20-30 minutes before: Another 8 oz if you're thirsty. That's it. You don't need to overdo this part.
If you're running longer than 60 minutes, or it's hot out, add electrolytes to that pre-run water. Sodium especially matters here, it's what helps your body retain the fluid you're drinking instead of just peeing it out an hour later. Sodium is also especially important for muscle function.
During Your Run
This is where most runners get it wrong in one direction or the other.
Under 45 minutes: You probably don't need to drink at all unless it's brutally hot. Your body has enough stored fluid to get you through your run.
45-90 minutes: 4-6 oz every 15-20 minutes. Don't wait until you're thirsty to start, that just means you're already behind.
Over 90 minutes: Same 4-6 oz every 15-20 minutes, but now electrolytes matter as much as water does. Plain water alone on long runs can actually dilute your sodium levels, and that's more dangerous than mild dehydration. This is where a sports drink or electrolyte tab earns its spot in your hand.
Quick gut-check: pale yellow urine means you're in good shape. Dark yellow means drink more. Clear as water means you're probably overdoing it.
After Your Run
This is the step most people skip, and it's arguably the one that matters most for how you feel the next day.
Weigh yourself before and after your run. Not glamorous, but it's the most accurate way to know your sweat rate. For every pound you lost, drink 16-24 oz over the next couple hours. Don't slam it all at once, your body can only absorb so much fluid per hour. Chug it too fast and you're just running to the bathroom instead of actually rehydrating.
Get sodium back in your system. If you sweated heavily or ran in the heat, plain water isn't going to cut it. A recovery drink with electrolytes, or just salting your post-run meal, helps your body hold onto that fluid instead of flushing it right back out. For every pound of sweat lost, you should be taking in 200-400 mg of sodium.
Eat something with water content. Fruit, soup, a smoothie — these support rehydration alongside plain water, and they give you the carbs and protein your body needs for recovery anyway.
The Bottom Line
There's no magic number here, because your needs change with distance, heat, and your own sweat rate. But if I had to give you a universal rule: hydrate steadily before you run, sip consistently on anything over 45 minutes, and rehydrate deliberately afterward based on what you actually lost.
Pay attention to how your body responds. That's how you build a hydration strategy that actually works for you — not one pulled from a generic chart online.
If you want help dialing in your training, fueling, and recovery around your specific goals, that's what we do at Glide.
Josh Kober is the co-owner of Glide Training Co. in San Diego's Bankers Hill neighborhood. He has been training runners of all levels for 15 years., studied exercise science at CSU, Long Beach, and has been helping people recover from injury since 2012.