More info:<br><br>I found a reference in my notes that modern charcoal (activated carbon) cannot be renewed. Bone charcoal, which was once used in the aquarium hobby, could be renewed, but I don't have notes on how to do that.<br><br>Also, I noticed that the flow rate could affect efficiency. The slower the flow rates the better to allow the carbon to bind to the chemicals. The person who installed the two-filter system I referenced, also stated that the filters were not particularly effective in removing chlorine and chloromine. So this may be evidence that carbon may not filter out all foreign chemicals. Hence, I would not rely upon it solely as a source for safe water under emergency situations.<br><br><br>Willie Vannerson<br>McHenry, IL