Most travellers’ stomach trouble is a water and handling problem

The mechanism is simpler than the folklore

Traveller’s stomach upset is overwhelmingly caused by swallowing organisms that came from somebody’s gut and reached your mouth by way of water, hands, surfaces or food that was handled after cooking. That is the whole chain, and every sensible precaution is an attempt to break it at one point or another.

It is not caused by spice, by unfamiliar cuisine or by the general fact of being abroad, which is a persistent belief worth putting aside. Newcomers do sometimes react to a much richer or hotter diet than they are used to, and that is a real but separate discomfort with a different cause.

Locals are not immune either, they are simply exposed continuously and have adapted to the particular organisms in their own environment. Somebody moving between Indian cities can have the same trouble that a foreign visitor does, which tells you the issue is exposure rather than nationality.

Water is the largest single variable

Municipal supply quality varies enormously across India and cannot be assumed safe to drink untreated. Bottled water is widely available, and so is filtered water from dispensers in hotels and restaurants, which is generally reliable and produces far less plastic waste than the alternative.

A refillable bottle with a decent filter or a purification method covers most situations and removes the daily decision entirely. Boiled water is safe once it has actually boiled and cooled in a clean container, which is why tea is a reasonable default in places where the water is uncertain.

Ice deserves separate thought, since frozen contaminated water is still contaminated. Commercially produced ice is common and generally made from treated water, but it is not always what is in the glass, and in a small establishment it is worth asking or declining. The same applies to anything mixed with untreated water.

Handling after cooking is the second one

Heat deals with most of the problem, which is why freshly cooked food served hot is a good bet almost anywhere. The risk concentrates in what happens afterwards: cooling, standing, being handled, being rinsed in untreated water or being cut on a board that was not clean.

That points to turnover as the most useful signal available to a visitor. A busy place cooking to order is safer than a quiet one with prepared dishes sitting out, regardless of how either looks. A stall with a queue of regulars has a stronger incentive and a faster cycle than a place trading on passing visitors.

Your own hands are part of the same chain and are the part you control completely. Washing before eating, or using a sanitiser when there is nowhere to wash, is the cheapest single intervention available, and it matters more in a food culture where eating with the hand is normal.

Travel itself makes it more likely

Long journeys interfere with sleep, hydration and routine, and a tired, dehydrated traveller eating at odd hours in unfamiliar places is more likely to have a bad few days than the same person at home. That is not a medical claim about immunity, just an observation about how these trips actually go.

Stations, bus stands and airports are also where the least appealing options tend to be, at exactly the moment when you are hungry and have twenty minutes. Carrying something sealed and simple for those moments removes a whole class of decisions made under time pressure.

Heat is a compounding factor. In hot weather prepared food deteriorates faster, and a dish that would be fine for two hours in a cool climate is not fine for two hours in an Indian summer. This is one reason the freshly-cooked rule matters more here than in temperate places.

What to do about it, within limits

This is not the place for medical advice, and it should not be treated as such. The general position is that most episodes are short and self-limiting, that fluids matter more than anything else during one, and that oral rehydration salts are cheap, widely available and worth carrying.

What does need a doctor is anything beyond that: high fever, blood, severe pain, symptoms lasting more than a couple of days, or illness in a child, an older traveller or anybody with an existing condition. Self-medicating with antibiotics picked up over a counter is a poor idea for reasons that go well beyond the individual.

Vaccination and any prophylaxis are questions for a travel clinic before departure, with recommendations that depend on where you are going, for how long and on your own history. They also change, so current advice from a qualified source is the only version worth acting on.