It is very important to stay hydrated while you are in Bangkok, because the Thai capital can be sweltering hot and humid. The temperatures can reach 40 degrees at the hottest point of the year and along with the pollution it is very important to avoid dehydration. But do you need to keep yourself stocked up with bottled water at all times-- that will cost around 40-60B a day.
Although the water that is produced by the water authority in Bangkok is perfectly drinkable when it leaves the plant, it will usually travel through old, dirty and broken pipes before it reaches your tap. This is how the water in Bangkok can become contaminated and not safe to drink.
Thais use peanut oil in a lot of their cooking. While you can try to explain to your waiter that you can't come near peanuts in any form before you order, to be sure they really understand, we'd suggest getting staff at your guesthouse or hotel to write you a note in Thai explaining your requirements. Select wisely has some rather neat pre-printed cards to deal with various allergies.
Aside from peanut oil, peanuts are also used in some of the cold salads, satays and pad thai -- the latter sometimes more as a garnish than as a part of the dish.
You should probably be fine, though you will need to take more care with you're eating. Select wisely has some rather neat pre-printed cards to deal with various allergies.
If you are allergic to a wider range of foods and don't have enough Thai language to make your requirements clear, you may be better off to take advantage of the fact that Thailand has a fine selection of international eateries so you should be able to find what you'd normally be eating at home. Even in upcountry provincial Thai capitals you should be able to get pretty basic Western staples.
Absolutely, though you'll need to look around a bit to find it sometimes - especially in the smaller rural centre.
Chiang Mai has a particularly good reputation for vegetarian food with Bangkok running a close second. You'll also find a pretty good range of western vegetarian outlets in most tourist centre like Ko Samui or Phuket.