well there are many health effects you can talk about... vomiting, diarrhea, various other forms of sickness often prokaryotes or bacteria will cause the contamination... this is normally taken care of in places that have a water treatment facility to filter out all that nasty stuff they can spread in various ways from one person to the next but one of the most common is the fecal-oral route, meaning that the disease can be spread is someone ingests something that has somehow come into contact with the feces of a person who has the disease