Impossible to say. People will swear they got sick eating at the Intercontinental in Bangkok and then someone will be along to say they slept in a gutter in Pataya for a year, drinking out of puddles, and were fine. Anecdotally, I go there a lot (we live in Asia so Thailand is our shorthaul beach destination), I've never been sick there, but I also go to India a lot and have never been sick there either, despite not being super careful (I take ice in drinks and brush my teeth in tap water). However, a lot of hotels and villas now have their own filter systems for tap water to avoid plastic waste so it's less of an issue than it was. .
Hi, I have lived in southeast Asia for quite a number of years, and to reassure you, I have only had extremely bad food poisoning one time. I am very small, I weigh about 36 kg, so I try very hard to avoid getting sick. The year I did get sick I dropped to 32 kg and it took me quite a while to get well. And street food is fine, just pick a place where there are many people and the food is turning over quickly. If you want ice cream, just find one of the ice cream chains like swensen. In Thailand, most of the shopping malls have food courts as well and a lot of people like to eat in there.
Many years ago, I remember an elderly expat in South East Asia telling me it was fine to brush your teeth in the tap water as long as you remembered to spit well!
I have stuck by that advice for years and haven't ever got sick. Like another poster, I've never been sick in Thailand, but haven't ever been sick in India either, where lots of people do have problems. I think it definitely helps that I don't eat meat. I'm also careful about ice cream, bottled water, ice and salad.
I live in Thailand and I would say diarrhea is more likely than vomiting. Like the others say, bottled water. Ice if it’s got a hole in it. I use tap water to brush my teeth (but I don’t swallow the water), my husband prefers to use bottled water. Ice cream - if you’re being careful the. Stick to the packaged ice cream but it should be fine. And like hello kitty says, enjoy the street food but go somewhere where there is a good turnover and where Thai people are eating. Have a wonderful time - this country is fabulous!