Cryptosporidium is waterborne parasite that sizes over 4 microns. It lives in a hard leathery shell and causes severe flu-like symptoms when ingested. Once they are in the human stomach, the hard shell is softened with the digestive fluids. Four protozoa living inside the cyst are broken free and allowed to reproduce and live in the human body. They are mainly found in the small intestine where they corrode the walls as they multiply. 

 As a result of the deterioration of the lining of the small intestine, the human body is unable to absorb water and nutrients. This causes the infected person to expel the outer shells of the cryptosporidium through vomiting and diarrhoea. It is estimated that an infected person would produce about 100 million of the outer shells per day.

When the parasite is ingested, it takes about 2 to 12 days for the protozoa to hatch. During this period, the patient will not have any symptoms of the illness. After that period, the illness takes course giving the patient extreme discomfort from 10 to 14 days and can sometimes last up to even 6 months. Nobody can be immune to this illness, but a healthy person can eventually recover. However, for individuals with weak immune systems including elderly, infants, chemotherapy patients, organ transplant recipients and AIDS patients it could be fatal as the parasite can also infect other organs. This would result in malnutrition and extreme dehydration.

Another commonly known cyst is Giardia which is also of risk to the human body. In the last 10 years, this has been a major subject of concern in tap water. Unfortunately, it is one of the most resistant parasites to water chemical treatments ever encountered. To date, cryptosporidium can be removed only by filtration and many municipal filtration plants are not efficient enough to take them out. This results in the existence of the parasite in the drinking water at homes.