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.
Definition of canonical for English Language Learners. : 1  connected with or allowed by the laws of the Christian church. : 2  of or relating to the books that are considered to be part of a religion's official text. : 3  of or relating to the group of books, plays, poems, etc., that are traditionally considered to be very important.