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. 1 : of, relating to, or forming a canon canonical scriptures. 2 : conforming to a general rule or acceptable procedure : orthodox His proposals were generally accepted as canonical. 3 : of or relating to a clergyman who is a canon.