Why water purifying ?? Have you ever heard about Legionella and legionaires disease, If not you should read this here
The genus Legionella is a pathogenic group of Gram-negative bacteria,
that includes the species L. pneumophila, causing Legionellosis (all illnesses caused by Legionella) including a pneumonia type illness called Legionnaires' disease and
a mild flu like illness called Pontiac fever.
The side-chains of the cell wall carry the bases responsible for the somatic antigen specificity of these organisms. The chemical composition of these side chains both with respect to components as well as arrangement of the different sugars determines the nature of the somatic or O antigen determinants, which are essential means of serologically classifying many Gram-negative bacteria.
Legionella acquired its name after a July 1976 outbreak of a then-unknown "mystery disease" sickened 221 persons, causing 34 deaths. The outbreak was first noticed among people attending a
convention of the American Legion—an association of U.S. military
veterans. The convention in question occurred in Philadelphia during the U.S. Bicentennial
year in July 21–24, 1976. This epidemic among U.S. war veterans, occurring in the same city as—and within days of the 200th anniversary of—the signing of the Declaration of Independence, was widely publicized and caused great concern
in the United States.
On January 18, 1977, the causative agent was identified as a previously unknown bacterium subsequently named