NSF develops their standards in collaboration with national arbitrators such as the Environmental Protection Agency (EPA) and are accepted by the American National Standards Institute (ANSI).
When it comes to home and commercial water filters, NSF has led the development of the American National Standards (ANS) since the 1970s. While manufacturers aren’t legally required to submit their products for NSF evaluation, those that do are subjected to rigorous testing in their Michigan-based labs.
Aside from the NSF, there are other reputable water testing boards, including The International Organization for Standardization based in Switzerland. All major testing or certification bodies, including the ANSI, WQA, and the CAN in Canada, certify products against NSF codes.