Source of VirusesViruses are infectious organisms that range in size from 10 to 25 nanometers [1 nanometer one billionth (10-9) of a meter]. They are particles composed of an acidic nucleus surrounded by a protein shell. Viruses depend totally on living cells and lack an independent metabolism. There are over 100 types of enteric viruses. Enteric viruses are the viruses that infect humans. Enteric viruses, which are of particular interest in drinking water, are hepatitis A, Norwalk-type viruses, rotaviruses, adenoviruses, enteroviruses, and reoviruses. The test for coliform bacterial is widely accepted as an indication whether or not the water is safe to drink; therefore tests for viruses are not usually conducted. The US EPA has established an MCL that states that 99.99% reduction or inactivation for viruses. Major enteric viruses and their diseases are shown below.
Enteroviruses (Polio, Aseptic meningitis, and Encephalitis)
Reoviruses (Upper respiratory and gastrointestinal illness)
Adenoviruses (Upper respiratory and gastrointestinal illness)
Hepatitis A (Infectious)