The tap water in Thailand is not safe to drink. Drink only bottled water or from a flask supplied from the hotel. Water provided in resturants is safe, but if you go out to a street kitchen to eat drink only water from a bottle. Most street kitchen use tank water, this is good for Thais who are used to the bakteria but not for the turist.

The ice is most of the time very safe, but do avoide the "shaved" ice from the road side stalls.

Due to the climate in Thailand it is recomended to drink at least 2 liter of water per person and day.