I don't really think that is possible. The only way I'm aware of to "reactivate" carbon involves burning it at extreme temps in the absence of Oxygen... Basically the same way it's made. I do know you can get back *part* of the adsorbancy by baking it in the oven. But it really wasn't much and not worth the stench it made. I did a food coloring test, just take some used carbon and split it into 2 batches (Use a third of new carbon for a control). Now make up one large batch of water and food colouring and split that into 3 even batches. You want just enough food colouring to tint the water darkly but not enough to make it so you can't see through it. Then dump in the carbon and give it a few good shakes. Compair all in a well lite area with a white paper for the background.
It's been a long time but I *think* it was 1/2 cup carbon, 1L (4 cups) water and either a half or one tsp of blue food colouring per each test. Someone I know did this too and didn't see any difference even with the same brand of carbon. They did however use a different brand of food colouring. Perhaps the concentration was much higher?
Anyway, try it you'll know pretty quick if coldwater rinsing does anything
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Chris