NSF certifies drinking water filters to standards applicable to each type of treatment option. You may notice the NSF mark on a product along with numbers such as NSF/ANSI 53 or NSF/ANSI 42, which refer to the standard to which the filter has been certified.
The definition of a canon is a principle, law or standard by which people are judged or a member of the clergy living according to these principles or laws. An example of a canon is a moral principle that a group believes is correct or proper.
A classic is a book accepted as being exemplary or noteworthy, for example through an imprimatur such as being listed in a list of great books, or through a reader's own personal opinion.he terms classic book and Western canon are closely related concepts that can confuse the student of literature but that are not necessarily each identical with the other. A canon refers to a list of books considered to be essential and is presented in a variety of ways.