Do you have difficult contaminants in your water like arsenic, nitrates, Hexavalent Chromium, then a Reverse Osmosis water filter system is what your looking for to resolve your worries. Difficult inorganic contaminants that are toxic and dangerous to consume require the additional protection gained from a reverse osmosis membrane. The Watts 525 Reverse Osmosis is a premium RO system that has been tested and certified by NSF International against NFS / ANSI Standard 58 for the reduction of Arsenic, Barium, Cadmium, Copper, Cyst, Fluoride, Hexavalent Chromium, Lead, Radium