There is no universal number, and any brand that gives you one is guessing on your behalf. Two people walking the same trail at the same pace in the same heat can lose fluid at two to five times different rates, and sodium at five to ten times different concentrations.
So this is not a prescription. It is how to work out your own, what changes past the three-hour mark, and one safety point that matters more than everything else here — including, bluntly, more than whether you buy an electrolyte drink at all.
Why the numbers on the back of the pack cannot be right for you
Two variables, both enormous.
Sweat rate runs roughly 0.5 to 2.5 litres an hour across exercising adults, and higher in extreme heat. The most-cited outlier is a marathoner measured at 3.7 litres an hour. Humidity matters as much as temperature: in humid air sweat cannot evaporate, so you produce more of it for less cooling — sweat that runs off you is wasted water.
Sweat sodium concentration runs roughly 20 to 80 millimoles per litre — about 460 to 1,840mg of sodium per litre of sweat — with individuals measured outside that band on both sides. Baker's normative data is the reference set here.
Multiply the two together and the spread is enormous. A light sweater losing 0.7L an hour at the dilute end loses a few hundred milligrams of sodium an hour. A heavy, salty sweater at 2L an hour loses several grams. Same hike.
Your number is roughly stable but not fixed. It is reproducible enough for individual sweat testing to be worth doing, and it shifts with heat acclimatisation, your dietary sodium, and your sweat rate itself. A field test is a snapshot, not a constant.
How to find yours, for free
Weigh yourself naked before a hard hour, and again after, and account for anything you drank. A kilogram lost is roughly a litre of sweat. Do it two or three times in different conditions and you will know more about your own hydration than any product page can tell you.
The salt side is harder to measure at home, but you have proxies: white crusting on your face and clothing, stinging eyes, and a persistent craving for salty food afterwards all point toward the salty end of the range.
When does sodium actually start to matter?
Softer than the marketing implies, and the honest answer has three variables rather than a threshold.
- Under about 60–90 minutes in temperate conditions, plain water is fine for most people. Your sodium losses are small against your body's stores, and dinner covers them.
- Past about two hours, and especially in heat, cumulative losses become large enough to be worth replacing — the ACSM position stand frames sodium replacement as most relevant beyond two hours, in heat, and for salty sweaters, without setting a universal cutoff.
- If you are a heavy or salty sweater, all of the above arrives earlier.
Anyone telling you sodium starts mattering at exactly ninety minutes has invented a precision the evidence does not contain.
The safety section, which we are putting above the shopping advice
Exercise-associated hyponatraemia is low blood sodium caused during prolonged exercise. It is uncommon, it is serious, and the intuitive response to it makes it worse.
Exercise-associated hyponatraemia (EAH) — blood sodium falling below the normal range during or shortly after prolonged exercise. Severe cases can cause brain swelling and are life-threatening.
It is primarily caused by drinking too much, not by losing too much salt. That is the finding of the Third International EAH Consensus Development Conference, and it is the opposite of what most people assume. Taking in more fluid than you are losing dilutes the sodium already in your blood — and sports drinks are far too dilute relative to blood to protect you, so switching from water to an electrolyte drink is not the answer either.
Who is most at risk, per the consensus statement: events longer than four hours, hot conditions, smaller body size, slower pace, inexperience, and unlimited access to fluid. Read that list again if you are planning a long, slow day in the heat with plenty of water available. That is a hiker's profile far more than a fast marathoner's.
The clearest warning sign is gaining weight during the event. If you finish heavier than you started, you drank more than you lost. Other signs: bloating or puffy fingers, nausea, headache, dizziness, confusion. In severe cases, vomiting, altered mental state, seizures.
Those symptoms overlap almost completely with dehydration and heat exhaustion, and that is exactly what makes this dangerous.
⚠️ If someone is symptomatic after a long, hot effort, do not treat it by giving them more fluid — water, sports drink or ours. Get medical help. In hyponatraemia, more hypotonic fluid can precipitate life-threatening brain swelling. The real treatment is a medical intervention, not something to attempt on a trail. A company selling electrolyte powder telling you to drink less of it is not a marketing move; it is the actual guidance.
Drink to thirst, or drink to a schedule?
The consensus has moved, and it moved for this reason.
Through the 1990s and 2000s the advice was to drink ahead of thirst, on the grounds that thirst lags dehydration. The EAH consensus traces documented cases directly to that advice: 41 cases of athletes who deliberately over-drank because they had been told thirst was unreliable.
Current guidance is drink to thirst, and never drink with the intention of gaining weight during exercise.
A 2018 review in Sports Medicine reconciles the two camps sensibly. Thirst is a well-regulated mechanism and the right default for most people in most conditions. Planned drinking has a narrower legitimate use: high sweat rates, real heat, sustained hard efforts, where drinking only to thirst tends to replace roughly half of what is lost. That is a competitive athlete racing in heat, not someone walking at conversational pace with a full bladder pack.
Two honest caveats: thirst is a poorer guide during very hard efforts when you cannot easily drink, and it can blunt over many hours of ultra-distance.
Carbohydrate, which matters more than most people expect past two hours
Distinct from the fluid question and better defined.
| duration | carbohydrate per hour | notes |
|---|---|---|
| Under 45 min | None needed | Stored glycogen covers it |
| 45–75 min | Small amounts, or even a mouth rinse | The effect here is partly central, not fuel |
| 1–2 hours | ~30g | Any single carbohydrate source |
| 2–2.5 hours | Up to ~60g | Around where a single transporter saturates |
| Over 2.5–3 hours | Up to ~90g | Needs mixed sources — glucose plus fructose |
That last row is the useful, under-known one. Glucose absorption is limited by one intestinal transporter that tops out near 60g an hour. Fructose uses a different one, so combining sources roughly doubles the gut's total capacity — and in controlled trials mixed-source drinks produced better endurance performance than glucose alone at matched total intake.
Below about 60g an hour this is irrelevant. It only matters when you are trying to take in a lot.
Note what this means for any electrolyte drink, ours included: at 5g of carbohydrate a serving, it is not your fuel. Food is your fuel.
Heat, and why early season is worse
Heat raises both your sweat volume and your total sodium loss.
But you adapt. Heat acclimatisation makes your sweat more dilute — your body gets better at reabsorbing sodium before the sweat reaches the skin, an effect documented as a linear decline in sweat sodium concentration with repeated heat exposure. Most of the adaptation lands within seven to fourteen days.
Practical consequence: the same person on the same trail is a saltier, thirstier proposition in the first week of a heat wave than a fortnight later. If your first big day of the summer feels disproportionately hard, that is a real physiological reason and not a character defect.
Hiking specifically — and an honest note about the evidence
Most sports science on hydration is done on runners and cyclists. There is comparatively little controlled research on hiking as its own activity, and anyone presenting hiking-specific prescriptions with confidence is extrapolating. The best available consensus document covering this ground is the Wilderness Medical Society's practice guidelines on heat illness.
What genuinely distinguishes a long day on foot: it is low intensity but very long, sun exposure is unrelenting, altitude adds respiratory water loss and can blunt thirst, and you are usually carrying your own water — which means fluid access is easy and unlimited.
Which puts hiking, uncomfortably, right in the EAH risk profile from earlier. For most day hikers the more realistic error is drinking too much, too dutifully, over too many hours, rather than not drinking enough.
Four things this category oversells
Salt tablets to prevent cramps. Modern controlled work does not support it — cramping tracks fatigue and pace far better than it tracks electrolytes. We went through that evidence properly here, including the part that does survive.
Pre-loading or hyperhydration. The evidence for meaningful performance benefit is weak and inconsistent, and it does not substitute for managing fluid during the effort.
Electrolytes for short sessions. For an hour in a temperate gym, water is fine. There is nothing wrong with drinking electrolytes anyway; there is something wrong with a company telling you that you need them.
Alkaline and "structured" water. No credible mechanism, no evidence base. A marketing category rather than a physiological one.
Frequently asked questions
Do I need electrolytes for hiking? Past a few hours, in heat, or if you are a salty sweater, they are worth having. For a cool two-hour walk, water and lunch cover it.
How much water should I drink while hiking? Enough to satisfy thirst, and not so much that you finish heavier than you started. Population ranges land around 400–800ml an hour in moderate conditions, but individual sweat rates vary several-fold — measure your own.
How much sodium do I need per hour of running or cycling? Roughly 300–700mg an hour is a reasonable population midpoint in moderate conditions, and heavy salty sweaters can need well over 1,000mg. These are averages of very different people, not a prescription.
Are electrolyte drinks better than water for long hikes? For efforts past a couple of hours, yes — for replacing sodium and for retaining fluid. Below that the advantage is small and mostly a matter of preference.
Can you drink too much water on a hike? Yes, and it is more dangerous than mild dehydration. See the hyponatraemia section above; weight gain during the day is the clearest warning sign.
Do I need electrolytes for a one-hour trail run? No. Water covers it in most conditions.
Where Snake Oil fits — with the arithmetic shown
One stick in 16 ounces of water delivers 370mg of sodium, which works out to roughly 780mg per litre of drink, along with 5g of carbohydrate, potassium, magnesium, zinc, the B lineup with vitamins C and E, and a glutamine-led amino acid blend.† It also carries 100mg of caffeine — useful on a long day, worth knowing about if you are sensitive or finishing late.
Now hold that against the numbers above. A moderate sweater losing a litre an hour at 1,000mg of sodium per litre is down roughly 1,000mg in that hour. One stick replaces a bit over a third of it.
So: one stick is one sensible dose, not an hour's replacement for a heavy salty sweater on a hot day. If that is you, you need more of something — more sticks, salty food, or both — and you should know that from arithmetic rather than from a slogan.
Your food is your fuel. Your thirst is your guide. This is one input into a day you are managing yourself.
†These statements have not been evaluated by the Food and Drug Administration. This product is not intended to diagnose, treat, cure, or prevent any disease.
Related reading: Electrolytes before or after a workout? · Does dehydration cause muscle cramps? · Post-workout recovery drink: what actually matters