Waterborne illnesses. You can get infections which are passed via the fecal oral route such as giardia, cryptosporidium, hepatits A, norovirus, camplobacter, Salmonella, and E. Coli most of which cause gastroenteritis with diarrhea and cramping. http://www.cdc.gov/healthywater/drinking/public/water_diseases.html.
Many. Many infections but generally those related to protozoa (such as amebiasis, cryptosporidiosis, giardiasis, microsporidiosis), parasites (such as schistosomiasis, teniasis, ascariasis, enterobiasis), bacteria (such as cholera, botulism, E. coli infections, dysentry, typhoid, salmonellosis) and viral (such as polio and hepatitis).