Care in what you eat and drink is the most important health rule;

Stomach upsets are the most likely travel health problem (between 30 and 50% of travellers in a two-week stay experience this), but the majority of these upsets will be relatively minor. Don't become paranoid; after all, trying the local food is part of the experience of travel.

Water & Drinks
If in doubt, the number one rule is don't drink the water, and that includes ice. If you don't know for certain that the water is safe, always assume the worst. Reputable brands of bottled water or soft drinks are generally fine, although in some places bottles refilled with tap water are not unknown. Only use water from containers with a serrated seal - not tops or corks. Take care with fruit juice, particularly if water may have been added. Milk should be treated with suspicion, as it is often unpasteurised. Boiled milk is fine if it is kept hygienically and yoghurt is always good. Tea or coffee should also be OK, since the water should have been boiled. Remember to clean your teeth with purified water rather than straight from the tap.

Water Purification
The simplest way of purifying water is to boil it thoroughly. Vigorously boiling for five minutes should be satisfactory; however, at high altitude water boils at a lower temperature, so germs are less likely to be killed.

Simple filtering will not remove all dangerous organisms, so if you cannot boil water it should be treated chemically. Chlorine tablets (Puritabs, Steritabs or other brands) will kill many pathogens, but not those causing giardia and amoebic cysts. Iodine is very effective in purifying water and is available in tablet form (such as Potable Aqua), but follow the directions carefully and remember that too much iodine can be harmful.

If you can't find tablets, tincture of iodine (2%) or iodine crystals can be used. Four drops of tincture of iodine per litre or quart of clear water is the recommended dosage; the treated water should be left to stand for 20 to 30 minutes before drinking. Iodine crystals can also be used to purify water but this is a more complicated process, as you have to first prepare a saturated iodine solution. Iodine loses its effectiveness if exposed to air or damp so keep it in a tightly sealed container. Flavoured powder will disguise the taste of treated water and is a good idea if you are travelling with children.

Food
There is an old colonial adage which says: 'If you can cook it, boil it or peel it, you can eat it...otherwise forget it'. Salads and fruit should be washed with purified water or peeled where possible. Ice cream is usually OK if it is a reputable brand name, but beware of products bought from street vendors in developing countries and of ice cream that has melted and been refrozen. Thoroughly cooked food is safest but not if it has been left to cool or if it has been reheated. Shellfish, such as mussels, oysters and clams, and undercooked meat, particularly in the form of mince, should be avoided. Steaming does not make shellfish safe for eating.

If a place looks clean and well run, then the food is probably safe. In general, places that are packed with travellers or locals will be fine, while empty restaurants are questionable. The food in busy restaurants is cooked and eaten quite quickly, and there is less chance that it has been sitting around for ages and then reheated.

Nutrition
If the food available is poor or limited, if you're travelling hard and fast and therefore missing meals, or if you simply lose your appetite, you can soon start to lose weight and place your health at risk.

Make sure your diet is well balanced. Eggs, tofu, beans, lentils (dhal in India) and nuts are all safe ways to get protein. Fruit you can peel (bananas, oranges or mandarins for example) is always safe and a good source of vitamins. Try to eat plenty of grains (rice) and bread. Remember that although food is generally safer if it is cooked well, overcooked food loses much of its nutritional value. If your diet isn't well balanced or if your food intake is insufficient, it's a good idea to take vitamin and iron pills.

In hot climates make sure you drink enough - don't rely on feeling thirsty to indicate when you should drink. Not needing to urinate or the passing of very dark yellow urine is a danger sign. Always carry a water bottle with you on long trips. Excessive sweating can lead to loss of salt and therefore muscle cramping. Salt tablets are not a good idea as a preventative, but in places where salt is not used much, adding salt to food can help.