A virus consists primarily of a genome that replicates itself within a host cell by using its nucleic acids to direct the host cell to synthesize more viral nucleic acids and proteins.
All viruses have a protein covering which encloses the nucleic acid.
Some viruses also have a lipid-rich lipoprotein envelope over the protein covering. Members of the enteric viruses infect the gastrointestinal tract of humans and animals, and are excreted in feces. If the feces enter a surface water system, there is potential for the spread of waterborne disease. Enteric viruses of particular concern in water are hepatitis A, Norwalk-type viruses, rotaviruses, adenoviruses, enteroviruses, and reoviruses. HAV is readily transmitted through water.