>>>Chemical agents are just chemical contaminants that may be removed by charcoal filtration (SWAG).<<<<br><br>I don't have an answer to the specific issue on charcoal filtration, but I do know a few things to consider if you are relying upon it based upon info I've learned from keeping tropical fish.<br><br>Charcoal depends upon a poreous surface area to make contact with contaminents in order to bind them. Once "satuarted" the charcoal becomes ineffective. Worse yet, it may actually start to dump contaminents back into solution. So it's important to make sure your charcoal is clean.<br><br>One person I know has two in-line filters with a tap in between. He periodically tests the water from this tap for chlorine. Once it appears, he knows that the first filter is no longer effective so he replaces it with the filter from the second unit and put a new cartridge in the second unit. The second unit filters out contaminants from the first that get by the first before he has a chance to check the water. <br><br>He always puts in a fresh cartridge in the second unit (rather than only replacing the first unit's cartridge) so he never has to worry about testing the water after the second unit.<br><br>I also recall hearing about a technique to regenerate activiated carbon. I will try to see if I kept notes on that technique. Obviously, it's much better to use new cartridges but that my not always be possible in a an emergency situation.<br><br>Again, I must caution that this information is what I have learned from folks keeping tropical fish and I do not know if the same logic will apply towards maintaining safe drinking water.<br><br><br>Willie Vannerson<br>McHenry, IL