Re: What kind of organism is in the water in mexico. Why dous it make us sick.

Actually, there are a number of organisms that can affect us that live in 
the water we drink in Mexico (or other countries, or even situations - like 
flooding-). These would include varieties of:
*protozoans - (single celled organisms) 
      Amoeba (amoebic dysentery)
      Giardia
*bacteria - 
      E. coli
      Salmonella
      Camphylobacter
*Viruses

These can all affect our digestive systems - symptoms would include 
vomitting and diarrhea, intestinal cramping, flu-like symptoms.

People that live/are born in areas where the water is contaminated are 
often immune to the disease. Their immune systems have been exposed to the 
organisms for a long time in small amounts, and the antibodies produced 
against the organism by the immune system most likely protects them from 
the disease.