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 proper. 1  1 : the parts of the Mass that vary according to the liturgical calendar. 2  2 : the part of a missal or breviary containing the proper of the Mass and the offices proper to the holy days of the liturgical year.