Cryptosporidium is highly resistant to chlorine and other disinfectants, which are used to kill bacteria and viruses in drinking water. In addition, Cryptosporidium is so small that the type of filters used in conventional municipal water treatment does not easily remove it from the water. Over half of the tested public water supplies that use surface water have been found to have small amounts of Cryptosporidium in the water sent to homes and businesses. You cannot tell without expensive, special tests. These tests are not very good for home use, and are not always reliable.
Diarrhea can cause dehydration.
People with diarrhea should contact their health care provider who may recommend an oral rehydration therapy mix. Boil drinking water for at least three minutes. Avoid drinking water directly from lakes, rivers, ponds or stream. Avoid swimming in lakes, rivers, streams, ponds, public swimming pools or recreational parks. Avoid contact with feces of all animals, particularly young farm animals such as calves.