However, some filters also impregnate the activated carbon with an insoluble silver salt like silver chloride to act as a bacteriostat. This does not substantially kill bacteria in the water but does prevent its build-up and multiplication in the filter itself.

Silver chloride is toxic, though because it is insoluble, it would be hard to get a lot of it from the filter. Still, since the carbon particles could be carrying silver chloride, that’s another good reason to take the filter back to the vendor for replacement.

Remember, by the way, that a carbon filter alone mostly improves taste while removing some potentially harmful chlorinated hydrocarbons in tap water (which arise from the otherwise beneficial chlorination process). It does not make raw water bacteriologically safe. If you’re getting water from a municipal system, that’s usually not a worry, but if you getting it from, say, a well, you still need to have your well checked regularly for contamination.

The filter is defective, and the manufacturer has some explaining to do. Next time it happens – save the water in a mason jar – remove the filter – tape it to the mason jar – and hand it to the filter guy – demand a replacement.

You didn’t pay good money to be drinking black specks of carbon!