Per- and polyfluoroalkyl substances (PFAS) are persistent and widely distributed in the environment from commercial products and waste process residues, including in surface waters usually at low parts per trillion (ppt) levels. Groundwaters near contaminated locations can have higher parts per trillion or parts per billion (ppb) concentrations. Interim EPA Drinking Water Health Advisories (HAs) for perfluorooctanoic acid (PFOA) and perfluorooctanesulfonic acid (PFOS) that were originally 70 ppt were recently reduced to 0.004 and 0.020 ppt, respectively. Final HAs for perfluorobutane sulfonic acid and its potassium salt (PFBS) and hexafluoropropylene oxide (HFPO) dimer acid and its ammonium salt ("GenX chemicals") were established at 2000 and 10 ppt, respectively. The minimum reporting levels (MRLs) for PFOA and PFOS are currently 4 ppt. The scientific basis for these very low and unmeasurable HA values for PFOA and PFOS is debatable and up to about five orders of magnitude below many other worldwide national recommendations (e.g., Australia, UK, Canada), which are in the range of 100 ppt and above.