See Angkor and Die ...

Food Safety

Food Restaurant in Cambodia

Tap water throughout the country is not potable, so stick to bottled water. In restaurants, they should open the bottle in front of you. If not, send it back.

Ice is generally safe in the cities as well.

Hygiene is reasonable in the cities, but use common sense. If the cook (in the case of street food) is bodily clean — particularly their hands — then chances are the food is clean as well. For restaurants where the cook is not visible, the same type of thing applies. If the place and the employees are clean, then the place is likely okay. It’s nothing to worry about too much. If you do get a bug, it is very rarely life threatening and usually very easy to cure.