Product review (1 stars): these filters are useless.
I purchased a T.D.S. meter with these filters and did a control test with distilled water and it read (as expected 000).  I then tested the unfiltered well water at kitchen sink and it read 690 ppm).  Then I tested the refrigerator with your new filter (after purging the air and 2 gallons of water through the system) and it read 674 ppm.  A huge let down;  these filters are useless.