>>2836901
Usually I'm too cheap to buy bottled water. As long as the tap water has no discoloration, floating particles or horrible sewage taste, I'll drop in an Ef-Chlor tab and go on about my day. At eight cents per tablet, they're cheaper than buying a 1.5 liter bottle.
>>2836899
You can start after arrival by only eating foods that are bacteria-free, i.e. hot foods, fruits with rinds, etc. Then over time, you begin introducing the riskier foods.

There's no hard and fast solution. Sometimes you eat something a little dirty or fermented which introduces a good mix of bacteria, thus ensuring that you can eat like a local going forward and never get sick. The experience of getting used to a new set of gut flora can be quite uncomfortable. Grumbling noises, a bloated feeling, messy soft shits that burn your asshole on the way out, and mild cramps may all occur on a regular basis. Eating less food, and avoiding consumption of liquid for a couple hours after eating, helps concentrate your gastric juices, kill more bacteria and better process degraded/contaminated food.

That being said, if you ate something that irritates your stomach and ruins your appetite, the best solution might be to eat something else and push it along.