You think a lot about your guts when traveling in Africa and Asia.

Travelers, once they're home, may show photographs of the Taj Mahal and describe the roar of lions in the Serengeti. But on the road what they talk about is the state of their insides.

Not long ago, a group of travelers from around the world sat around the dinner table at a bhatti, a small inn-teahouse in Tirkhedunga, Nepal. A Scottish woman had apparently picked up giardiasis -- a diarrheal disease caused by a parasite carried by water -- before beginning her trek in the Himalayas. She was now hiring a horse to get her out of the mountains and to a clinic that could run tests to determine the appropriate treatment.

A young German man was prostrate on a bed in the inn while his friends described his symptoms and the steep descents and 2,000-foot climb that still lay ahead of them before reaching medical help.

In this part of the world, stories abound that "a lot of people get sick on the trek" or that "Happy Restaurant gives you the runs; go to Namaste Restaurant where they soak their vegetables in iodine."

The fact is that even in the United States, the giardia lamblia parasite has become a persistent problem in the last few years. It can be present in even the clearest of mountain streams, and the national park and forest services have issued warnings to hikers and campers that all water should be boiled for at least five minutes. In Third World countries, other parasites, as well as bacteria and viruses, can be present in water in any form (including ice and mixed drinks) that has not been boiled or purified.

Most people get sick because they ignore the advice that is standard for travel in the Third World: Drink water -- and milk -- only when properly boiled; drink nothing with ice in it; avoid all salads, fruits and vegetables that someone else has peeled; and eat only well-cooked food that is still hot from recent cooking.

In some cases, it is difficult for travelers to take this advice seriously. "On a recent trip to India with 12 other people, I told them never to drink the water," says John Baldwin, a University of Oregon environmental studies professor. "But in the nicest hotels, with spotless furnishings and elegant dining rooms, it was easy to forget -- or to convince oneself that there could not possibly be a problem. Twelve out of 13 on that trip got sick."

Another problem is the effort, nerve and persistence that it can take to ensure that the water you drink has really been boiled for five minutes or more. I once asked a waiter at a restaurant in Rangoon, Burma, whether his water was boiled. "Ah, no, sir, but it is filtered," he replied.

"That is interesting," I said. "How is it filtered?"

"Ah, sir, we strain it through a very special cloth." I ordered tea.

The best policy is to see the water actually boiling and then time it. Once, in Srinigar, Kashmir, I took a waiter's word for the fact that the drinking water was boiled. My traveling companion and I had dysentery for a week.

There are several ways to kill all bacteria (such as E. coli), parasites (including those in cyst form, like giardia lamblia) and viruses (like polio and hepatitis) that can be present in water:

Boiling the water for at least five minutes.

Proper use of tincture of iodine. (Iodine purification tablets, however, can lose their effectiveness once the bottle is opened. They also do not work as well with cloudy and/or cold water. Under standard conditions, one tablet can purify a quart of water in 30 minutes; with cloudy water, the use of two tablets is recommended; and cold water should be warmed and the contact time increased.)

Use of chlorine, although it is less reliable than iodine. (Its purification ability varies greatly, depending on the form of chlorine used, as well as the pH, temperature and organic content of the water.)

Commercial filtering devices. (These do not remove all organisms, however, particularly viruses, although a tiny amount of iodine can finish those off.)

Every method except boiling requires some degree of study and thought to make it reliable. For example, ascorbic acid is present in most fruit-flavored powders that people add to iodine-treated water to make it palatable. But it can stop the iodine from doing its work, so it must not be added until 30 minutes after the iodine.

If you choose boiling as a method, that's when effort, nerve and persistence come in. Many people in Africa, Asia and other Third World nations have no understanding of the reasons for boiling water. Some who have been exposed to tourists' requests for boiled water believe that these odd foreigners simply have a strange taste for drinking hot water. They therefore believe that "boiled water" means heated water and will say in all good faith that such water has been boiled when in fact it is merely hot.

On a recent camping safari in Tanzania, we had been assured that all water was boiled for 20 minutes. But when I talked to the Tanzanian cooks, they pointed to a pot of water that was just heating up, said with certitude "boiling" and removed it from the fire.

This is consistent with the flat advice of Stephen Bezruchka, author of "Trekking in Nepal": "I always assume that 'boiled water' has not been boiled, unless I have supervised it." That, however, can require some delicate diplomacy in the kitchen of a village teahouse, lest the proprietor take offense at your insistence on timing the boiling with your digital watch. "Don't you trust us Nepalis?" asked a young woman who had studied computers in the United States and was now at home with her parents at such a teahouse. "It's just a habit of mine," I explained feebly.

Whether you take such a personal role in assuring the cleanliness of your water and food may depend on how graphically you see the dangers. Stan Armington, the author of "Trekking in the Nepal Himalayas," says, "The germs that cause diarrhea are acquired mainly from {coming in contact with} someone else's stool."

This may occur not only by drinking contaminated water, but from food, dishes or utensils handled by people with poor sanitation habits.

I recently had a brief but unspoken battle of wills with a 10-year-old boy at a trekkers' lodge in Tatopani, Nepal. He had a habit of "cleaning" each Coca-Cola bottle after he opened it, by rubbing his finger over the rim. I ordered a Coke and picked up the bottle opener, but he quickly took it from me and started opening the bottle. I stood by watchfully as he pried at the cap. Just as the cap came off I reached for the bottle. But he was too fast for me, deftly sliding his fingers under the departing cap to make sure that I first received the good service of his finger wipe.

Even when you are careful to consume only properly boiled water and well-cooked food, when trekking you will quite likely eat off dishes that have been washed in contaminated, cold water. The utensils will have gone from someone else's mouth to a washing with dirty hands in contaminated water to your mouth. A few people take their own plates, but it is at least relatively easy to take along your own fork and spoon. A 73-year-old grandmother from Beverly Hills whom I met on the trail told me she hadn't been sick in four years of trekking by following such practices strictly.

Of course some water problems may be solved through the expertise of a major Western trekking or safari company. But even that may not be a full guarantee. "I tell my Tanzanian staff to boil the water for 20 minutes," explained an American safari leader for one of the world's oldest adventure travel companies. "But I also tell my clients to put tablets in the water. I just don't have the time to make sure it is all getting done properly. I can't be everywhere at once."

There really is no choice but to accept responsibility for your own insides and what goes in them.

John E. Bonine is a professor of law at the University of Oregon.