Most hikers know the risks of dehydration, but far fewer realise that drinking too much water can also be dangerous. Overhydration, particularly when it dilutes sodium levels in the body, can lead to a condition known as hyponatremia. It’s uncommon, but it can be serious, and I think it’s genuinely misunderstood and mismanaged on the trail more often than it should be.
This article forms part of the Trail Hiking Australia Hiking Safety Systems, within the Hydration and Fuel system. In that framework, I treat hydration as a balance problem rather than a volume problem, because fluid intake has to support cognitive function, temperature regulation, and safe decision-making without disrupting sodium balance. It’s that balance, not the total amount you drink, that actually protects your performance and safety out there.
So here’s what hyponatremia is, why it happens on hikes, how it differs from dehydration, and how to reduce the risk while you’re out on the trail.
What hyponatremia is
Hyponatremia occurs when the concentration of sodium in the blood becomes abnormally low. Sodium plays a critical role in nerve function, muscle contraction, and fluid balance, so when large amounts of plain water are consumed without adequate replacement of salts, sodium levels can become diluted, which disrupts all of that.
This condition is most often associated with prolonged activity, steady drinking over long periods, and situations where food or electrolytes aren’t being consumed alongside the water.
Why it happens on hikes
Hyponatremia typically develops during long or demanding hikes where people drink frequently but eat little, sweat heavily, or try to stay ahead of dehydration by forcing fluids. Hot weather, slower paces, and longer days can all contribute, particularly when hikers rely on plain water alone.
It can also happen when people misread early symptoms of fatigue or headache as dehydration and respond by drinking more and more water without stopping to reassess what’s actually causing how they feel.
Symptoms and why they are confusing
The symptoms of hyponatremia often overlap with those of dehydration, which is exactly what makes it difficult to recognise in the field. Common signs include headache, nausea, vomiting, fatigue, confusion, and in more serious cases, unsteady movement or altered behaviour.
Because these symptoms look so similar to dehydration, people often keep drinking water to try to feel better, and that can worsen the condition rather than resolve it.
Dehydration versus overhydration
Dehydration and hyponatremia can look similar, but they come from opposite problems. Dehydration results from insufficient fluid relative to loss. Hyponatremia results from fluid intake exceeding sodium replacement.
So if someone is drinking regularly, has access to water, and continues to deteriorate rather than improve, more water probably isn’t the solution. In that situation, slowing down, resting, eating, and reassessing intake makes more sense than continuing to drink large volumes.
Reducing the risk on the trail
The risk of hyponatremia can be reduced through balanced hydration practices. Drinking regularly rather than excessively, eating salty foods on longer or more strenuous walks, and replacing electrolytes when appropriate all help maintain normal fluid balance.
I’d avoid rigid rules such as forcing a set volume of water per hour, because hydration needs to be flexible and responsive to conditions, not mechanical.
The goal is fluid balance, not maximising intake. Drinking beyond thirst for long periods, especially without food or electrolytes, can dilute blood sodium even when total body water is high, and clear urine alone doesn’t guarantee safe hydration. That’s exactly why the amount you drink matters less than whether it stays in balance with sodium and food intake.
What to do if hyponatremia is suspected
If hyponatremia is suspected, stop exertion and reassess immediately. Do not continue forcing water. If the person can eat, salty foods may help, and rest is essential, though improvement may be gradual rather than immediate.
If symptoms are severe, worsening, or include confusion, vomiting, or loss of coordination, treat the situation as serious and seek medical assistance.
Hyponatremia is far less common than dehydration, but it’s real and it’s preventable, and most of the risk comes down to treating hydration as a balance problem rather than a volume one. Drinking too much water can be dangerous in the wrong conditions, and because it results from diluted sodium rather than fluid shortage, more water isn’t the fix once symptoms appear. Eating and drinking together, avoiding forced fluids on long or strenuous walks, and stopping to reassess if something feels wrong are usually enough to manage the risk, and understanding that is what lets hikers make better decisions about hydration on the trail.
Have you ever experienced symptoms that felt like dehydration while hiking? What did you do to manage it?