If a water filter carries the NSF International 53 or 58 certification, it has undergone independent testing and has been validated to decrease PFOA or PFOS levels to below 70 parts per trillion (ppt). While this is a good thing to look for, keep in mind that an NSF 53 or 58 certified water filter does not mean it can get rid of 100% of PFAS, and that it's only tested for 2 (out of 12K+) different PFAS.