On top of what has been written by @toy and @user34936, which I can support 100%, I would like to give you the following advice:
When traveling to remoter areas in Asia (I would count Laos into that), and specially if you do not do so frequently (several times a year), you are risking to get Diarrhea as a minimum and intestinal parasites as a worst case scenario where you run risk of severe organ damage in the long run. While the risk is, as mentioned, highest in India, there are 2 levels of caution that go along with the amount of inconvenience you have to face to execute them:
Easiest level, should prevail in most developing countries in Asia, can be ignored in Japan, mostly also in Hong Kong & Singapore for example:
- Do not drink Tap water
- Do not rinse your mouth with tap water after brushing your teeth (sounds stupid, but you always ingest some of it, and if you follow step 1, this is a direct consequence. That's why a lot of hotels in Asia have small bottles of water now standing next to the sink instead of in the room)
- Do not eat cold street food, specially fruits, ice cream etc.
Next level, should be observed in any remote, rural area of the developing countries outside of international hotel chains and in almost all of India:
- Do not eat any uncooked food, such as salads
- Do not eat unpeeled fruits and do never eat water melons. They are sometimes injected with water to make them heavier.
- Do not eat anything that has to have a consistent cooling chain without unfreezing such as ice cream, imported fish etc.
- Basically do not eat anything that is not served by established restaurants or hotels that you would find in a tourist guide.
- be very careful with ice cubes. Rather drink what has been cooled in a closed container such as cans & bottles than ice cubes.
The issue here is that you have to decide how much you want to reduce your flexibility in the country to avoid a light diarrhea and how much experience you have when traveling across the world in remote places. You body will build up resistance against a lot of bacteria types if ingested in small quantities. However I know a person who lived in China and other places such as Hong Kong for all their life who got a parasite in India that caused a almost 100% kidney failure and repeated operations over the following years. Also: While asking for bottled water might become quickly expensive since the hotels try to sell you Perrier etc, asking specifically for local bottled water is often a safe but very cheap alternative.
Also consider that Diarrhea as such might not bother you too much, but dehydration and other consequences of that issue might cause more trouble that might severely disrupt the trip for you.