Hydration And Electrolytes
How to stop guessing with bottles and salt
Hydration is one of those topics that’s either treated like a life-or-death science experiment or completely ignored until someone bonks on a long run and blames “just being unfit”. As usual, the useful bit sits quietly in the middle.
You don’t need to know your exact sweat rate to the millilitre. You also don’t need to wing every session and hope the odd sip from a bottle will cover it. The aim of this guide is to give you enough understanding to make calm, sensible decisions about fluid and electrolytes, so you feel better in sessions and don’t spend all day thinking about your next drink.
What you’re actually trying to do
When you train, you lose fluid and salt through sweat. The harder and hotter it is, the more you tend to lose. If you never replace enough, things slowly go downhill: your heart rate drifts up, pace drifts down, legs get heavier than they should, and your head starts to feel like it’s full of cotton wool. That’s dehydration doing its thing.
On the flip side, it is possible to overdo it. There have been races where people have drunk huge volumes of plain water “to stay hydrated”, only to end up with a sloshing stomach, multiple toilet stops and, in extreme cases, low blood sodium. That’s not the goal either.
What you’re aiming for is pretty modest: accept that you’ll always finish a long session a bit lighter, but give your body enough fluid and salt along the way that you can still think, move and perform properly. You’re not trying to replace every drop as it leaves; you’re just keeping the tank topped up enough that the system runs smoothly.
Everyday hydration: the boring foundation
Before you obsess over bottles on the bike, it’s worth checking the basics away from training.
If most of your day is powered by coffee, fizzy drinks and the occasional mouthful of water, you’re starting behind. You don’t need to chain yourself to a giant water bottle, but sipping fluids across the day instead of downing a litre just before a run makes a big difference. You shouldn’t be permanently gasping, but you also shouldn’t be surprised when a long session feels dire after six hours of zero drinks and three strong coffees.
Your body gives you fairly decent signals when you pay attention. If you’re always thirsty, always dry-mouthed and your pee is consistently dark, there’s room to improve. If everything is clear and you’re in and out of the loo all morning, you may be overdoing it. Most of the time, “somewhere in the middle” is fine. You don’t get bonus points for crystal-clear toilet water.
Once that everyday base is vaguely under control, then it’s worth looking more closely at what you actually drink during training.
How much to drink when you’re training
This is where people want a magic number, and unfortunately there isn’t one. Your sweat rate isn’t the same as someone else’s. It also isn’t the same in February as it is in a heatwave.
Even so, you can work with rough ranges instead of precise math. For shorter, easier sessions – the <60-minute easy run or the steady spin on a cool day – you often don’t need much more than what you’ve drunk beforehand and afterwards. Carrying a bottle and taking a few sips is fine if you like it; you’re unlikely to fall apart without some calculated intake.
Once you’re into longer or harder work, especially in warmer conditions, it helps to take drinking seriously. On the bike, where carrying fluid is easier, many athletes feel good aiming to work through something like a bottle an hour in warmer weather, sometimes less in the winter. On the run, it’s more of a juggling act: maybe you loop past home or the car, maybe you use a race belt or handheld, maybe you rely on aid stations. The goal is not perfection; it’s noticing the difference between “I drank something regularly” and “I ignored my bottle for two hours and now I feel like a raisin”.
You’ll know you’ve underdone it when you finish every long session with a pounding head, bone-dry mouth and that slightly zombified feeling that hangs around for hours. You’ll know you’ve gone too far the other way if your stomach has been sloshing like a washing machine and you’ve needed to dive behind every hedge on the route. The sweet spot is somewhere between those extremes.
Where electrolytes actually help
Sweat isn’t just water. When you see dried salt marks on your kit after a hot race, that’s sodium you’ve lost. Some people lose more than others, but no one loses none.
Electrolytes – usually in the form of tabs, powders or sports drinks – help replace some of that salt. They also help your body hold on to the fluid you’re drinking a bit better, rather than peeing it all straight out. What they are not is a source of energy. If you’re using electrolyte-only products, you’re sorting salt and fluid, not fuel.
The simplest way to think about it is this: water is generally fine for shorter, cooler, easier work. As sessions get longer, hotter or sweatier, it starts to make more sense to have something in the bottle that includes sodium, whether that’s an electrolyte tablet in water or a sports drink that combines carbohydrates and electrolytes. If you finish long summer sessions looking like you’ve been rolled in table salt, that nudge towards more structured electrolytes is even more useful.
You don’t need to take handfuls of salt capsules every hour just because an advert told you to. Start small, see how you feel, and adjust. If you’re someone who never cramps, never feels awful in the heat and generally feels fine, you don’t need to force it. If hot days routinely wipe you out, or you feel dizzy and hollow despite drinking loads of plain water, that’s a sign to bring electrolytes into the picture.
Choosing between water, tabs and sports drink
This is where the supermarket aisle gets overwhelming. Water, electrolyte tabs, isotonic drinks, energy drinks, “hydration mixes” – it’s a lot.
A simple way through it:
On easy days and short sessions, just drinking water around and after your session is usually enough. You’re not out long enough or hard enough to create a major fluid and salt deficit.
On days where the session is longer or the weather is warm, adding an electrolyte tablet to your bottle or using a carb-electrolyte sports drink gives your body more support. Tabs are useful if you’d rather get most of your carbs from food or gels; sports drinks can be handy if you like to get some of your fuel and fluid in the same place.
You don’t have to marry one product for life. Plenty of athletes use water or tea day-to-day, an electrolyte tab in longer or hotter sessions, and a full sports drink in races or big brick workouts. The “best” option is the one your stomach tolerates and you’ll actually remember to use, not the trendiest tub on Instagram.
Tuning things without turning it into homework
If you’re curious, you can get a more precise feel for your needs by doing a simple weigh-in experiment on a long session: weigh yourself (ideally with minimal clothing) before and after, keep track of what you drank, and see roughly how much weight you’ve lost. That gives you an idea of how much fluid you’re burning through in those conditions.
But you don’t have to do that to get benefits. For most people, a bit of awareness goes a long way. If your head always hurts after long runs, start bringing a bottle and actually drinking from it. If you feel bloated and uncomfortable every time you race, look at how much you’re necking beforehand “just in case”. If every hot day shreds you, experiment with adding electrolytes and see if recovery feels smoother.
The idea is to gradually nudge your approach in a better direction, not to turn every Sunday ride into a lab test.
Bringing it all together
Good hydration isn’t about being perfect. It’s about respecting the fact that fluid and salt losses matter, and giving your body enough support that training feels the way it should: hard when it’s meant to be hard, manageable the rest of the time.
Day to day, drink like a functioning adult, not a cactus. Around training, have a rough plan for when you’ll drink and what’s in the bottle, especially once sessions creep past an hour or the temperature climbs. Use electrolytes when they’re useful, not because you feel you “should”. Pay attention to how you actually feel, and adjust from there.
If you can get to a point where long runs and rides don’t end in a dehydration hangover, where races aren’t one long sloshy stomach, and where hot days feel survivable instead of catastrophic, then you’ve done more than enough. The goal isn’t to win the hydration Olympics – it’s to make training and racing feel better, so you can get on with the fun bit.