Use the EWG zip code search to find your water utility [1]. That shows which chemicals or toxins were found when testing your tap water, and scrolling down you

Use the EWG zip code search to find your water utility [1]. That shows which chemicals or toxins were found when testing your tap water, and scrolling down you see which filter system can remove those chemicals. For ex: San Francisco's City Water has Chromium (hexavalent) at 0.0906 ppb, and Total Trihalomethanes (TTHMs) at 38.9 ppb [2]. The "Water Filters That Can Reduce Contaminant Levels" table says Activated Carbon and Ion Exchange filtration can't remove those particles, but Reverse Osmosis can. [1]: https://www.ewg.org/tapwater/ https://www.ewg.org/tapwater/ [2]: https://www.ewg.org/tapwater/system.php?pws=CA3810011 https://www.ewg.org/tapwater/system.php?pws=CA3810011