For drinking water, buy a bottle of mineral water such as a convenience store.
Tap water is not drinkable by locals, so don't drink it.
Drink ice is basically safe because it is purchased from an ice shop, but you may want to avoid it.
(By the way, I've never heard of someone who had diarrhea with ice)
It is recommended to carry pocket tissue with you, as toilet paper may not be provided.
There is a water hose next to the toilet, and the locals wash their butt with water from this hose
(It feels like a Japanese electronic toilet.) Toilet paper cannot be washed out, please throw it in a large trash can next to the toilet.
Many people come to Vietnam to enjoy local food such as food stalls.
It is popular because it is cheap and delicious, but it is better to use it after wiping yourself with chopsticks, spoons, forks, plates, etc.
It is very convenient to bring a wet tissue.
Motorcycles are the most popular means of transportation in Vietnam.
Therefore, many people feel that the air is dirty with exhaust gas. If you are concerned about dirty air, walk with a mask.