Stick to bottled water. Bacteria in tap water can cause massive stomach upset and can carry giardia or a host of other unpleasant diseases. Bottled water is generally safe, but watch out for sketchy packaging. There have been a number of incidents where tap water was bottled locally. Check for a secure seal to increase safety.
Try iodine tablets. To reduce the environmental impact of bottled water, use iodine tablets or other water purification sources to rid your water of harmful bacteria. Use common sense: Iodine tablets are safer to use in mountain stream water, but they probably won't have much effect on tap water from a slum in Bangalore.
Shower with your mouth closed. It sounds surprising, but even a small amount of water from the shower can have disastrous ramifications later. You don't have to avoid showering to avoid Delhi Belly!
Exercise care when eating street food. There is no need to avoid it completely, but be cautious. Do not eat food that looks like it has been sitting out for a long time. Do not eat food that has flies on it. The safest street food is cooked or heated in front of you.
Choose clean restaurants. Excellent food can be found at grungy restaurants, but it's better to be safe than sorry. Choose restaurants where you can see your food being cooked, and you will reduce your chances of contracting Delhi Belly or other stomach upsets.
Avoid buffets. Food sits in buffet dishes for extended periods of time, thereby increasing the risk of harmful bacteria. Food that is cooked to order is almost always a safer option.
Order drinks without ice. Ice is a hidden cause of Delhi Belly because it often comes from unsafe tap water. Food safety extends to drinks.
Skip the raw vegetables and fruits. Though they look tempting, raw fruits and vegetables might have been rinsed with bacteria-laden tap water. A good rule of thumb is to eat only what you've peeled yourself. A whole orange is safe; a pre-peeled, sectioned orange may not be. Food vendors often sell whole fruits and vegetables for low prices, so you need not forgo fresh produce.
