Whenever I drink tap water, I get running stomach, but I have seen my neighbours drink the same water and not get any complications. Is there a problem with my stomach?
You have not clarified that whether you get running stomach each time you use tap water or it is sometimes. Is there associated nausea, vomiting and or abdominal pain? Untreated tap water is a potential source of infections of the stomach and intestines. These manifest as diarrhea, vomiting, abdominal cramps with fever sometimes. At time it may be severe enough to cause dehydration. The infections range from bacteria like salmonella, shigella, virus like rota virus and protozoa like amoeba, giardia, worms like ascaris. Severity of the manifest disease symptoms depends on quantity of the germs ingested and resistance of the individuals. If the load of germs ingested is high and resistance of the person is low there can be a severe disease. But if one has a good general health, that is, good resistance also, or the microbes ingested are few, there may be very mild symptoms.
These germs enter water through contamination by fecal matter. Now if one drinks this contaminated water, there is risk of infection entering the gut.
Some times allergy to certain kinds of foods can also cause diarrhea, though it may coincide with drinking tap water. Milk and meat products are usually implicated in such food allergies. One can also have a running stomach after being constipated for two to three days. Usually when an overloaded bowel empties there can be frequency of stools, which may be liquid or semi liquid in character. A running stomach can also occur due to consuming drinks with high sugar content. Mental stress is also one of the causes of running stomach what is known as irritable bowel syndrome.
My advice to you is to get a stool sample tested, if there are eggs or cysts (encapsulated forms) of any parasite or protozoa or any evidence of bacterial infection, it is curable with anti infective agents. Start using boiled or filtered water for drinking.