Depends on the filter. Some are nothing more than wound cord and they do nothing but remove particulate matter, sand, mud etc. They effect no change in the chemical composition of the water. Some contain granulated activated carbon. These will reduce chlorine and chloramine but will have no effect on dissolved ions. Still others, and the Brita is in this class, contain carbon and ion exchange resins. They remove chlorine and chloramine and dissolved ions. Then there are home water softeners, microfiltation systems, and RO units.