Traveler's Diarrhea: How to Rehydrate Properly

A stomach upset in the first few days of a trip is common enough to be almost unremarkable. Different water, different food handling, unfamiliar bacteria, and a gut that has not met any of it before. Most cases settle within one to three days without any treatment at all.

The part that actually causes harm is rarely the infection. It is the dehydration that comes with it — and that part is largely in your control.

Oral rehydration salts: why plain water is not enough

When you lose fluid through diarrhea or vomiting, you are not losing water alone. You are losing sodium, potassium, and other salts with it. Drinking only water replaces one half of that loss and dilutes what remains of the other half, which is why people who drink litres of water and still feel dreadful are not imagining it.

Oral rehydration salts — sold as sachets, and called ORS or oral rehydration solution once mixed — exist to solve exactly this. It is a specific balance of salt and sugar in water, and the sugar is not there for taste. Glucose and sodium are absorbed together through the intestinal wall, so the sugar is what carries the salt and the water across. That mechanism keeps working even when the gut is inflamed, which is why ORS remains effective during an active infection.

What to drink, ranked

Traveler's diarrhea treatment: what to eat, what to take

Long fasting is no longer the advice. Eating gently as soon as you can face it helps the gut lining recover. Start with plain starches — rice, bread, plain pasta, bananas, boiled potato — and leave dairy, fried food, and anything heavily spiced until you are clearly on the mend.

On anti-diarrheal medication: loperamide can be genuinely useful for getting through a flight or a boat transfer, but it treats the symptom rather than the cause. It should be avoided if there is a high fever or blood in the stool, since in those cases slowing everything down is the opposite of what you want.

Food poisoning treatment: when it stops being routine

Signs that dehydration is becoming serious rather than merely uncomfortable: passing very little urine or none at all, dark urine, dizziness on standing, a dry mouth with no saliva, sunken eyes, unusual drowsiness, or confusion. Confusion in particular is not a wait-and-see symptom.

Where IV fluids fit

For the great majority of cases, ORS is the answer and an IV adds nothing. It is worth being direct about that, because the opposite claim is easy to make and hard to justify.

The genuine exception is the person who cannot keep fluids down. Once vomiting means every mouthful comes back, oral rehydration stops working — and no amount of persistence changes that. Delivering fluid and electrolytes intravenously bypasses the stomach entirely, which is the one thing drinking cannot do.

Even then, fluids treat the dehydration, not the underlying infection. If the symptoms above point to something that needs diagnosis and treatment, that requires a doctor — and rehydration is a support measure alongside it, not a substitute for it.

Reducing the odds

• Drink bottled water only, and brush your teeth with it. Tap water will make you ill unless the property has an expensive filtration system installed, which most do not.
• Treat ice the same way. Commercially produced ice at established restaurants and hotels is fine; ice of unknown origin is not.
• Eat food that is hot and freshly cooked. Steam is a better signal than a menu.
• Be more careful with raw salads, unpeeled fruit, and anything that has been sitting out in the heat.
• Wash your hands before eating. It is unglamorous and it is the single most effective thing on this list.
• Pack ORS sachets. They weigh nothing, and wanting them at 2am is not when you want to go looking for them.