These do filter out some dissolved ions
I got this TDS tester, which measures how much resistance a current passes through water. If the water is highly pure, the resistance should be very high. But if there are dissolved ions, the resistance drop. The unfiltered tap water measures 171 PPM total dissolved matter. I then tested the regular brita filter, which also measures 171PPM. I read somewhere the regular brita filter does not has ion exchange resins so it will not filter out any dissolved salt or heavy metal ions. This filter, though, test out to be around 140 PPM after tap water passes through it. That means at least some ions got filtered out. Usually it's the heavy metal ion that's filtered out first, because each ion carries more charge. Sodium and potassium ions aren't going to be captured by ion exchange resin as efficient because they only have one positive charge. That's OK, since sodium and potassium ions are harmless anyway. I want the lead, cadium and other heavy metal ions gone, and this filter does that. Read more