Bacteria, viruses and cysts represent the three types of microbiological contaminants that may be found in water. Following this occurrence pattern, the NSF task group on microbiological standards has proposed a requirement that bacteria reduction claims are accompanied by tested claims of virus reduction and cyst reduction.
Links:
[1] http://admin.indiaenvironmentportal.org.in/feature-article/testing-water-treatment-products-bacteria-removal
[2] http://admin.indiaenvironmentportal.org.in/category/author/vaneet-gupta
[3] http://admin.indiaenvironmentportal.org.in/category/journal/everything-about-water
[4] http://admin.indiaenvironmentportal.org.in/category/thesaurus/water-treatment-technology
[5] http://admin.indiaenvironmentportal.org.in/category/thesaurus/drinking-water
[6] http://admin.indiaenvironmentportal.org.in/category/thesaurus/drinking-water-standards
[7] http://admin.indiaenvironmentportal.org.in/category/thesaurus/water-supply
[8] http://admin.indiaenvironmentportal.org.in/category/thesaurus/micro-organisms