The main reasons for black particles in Keurig water are black chips from the charcoal filter in the reservoir and coffee grounds that seep through into the cup. During shipping, the charcoal filter may suffer from shocks leading to chipping and dust sediments. These sediments will appear in your reservoir and might end up in your cup. Be sure to soak the filter cartridge in water for about five minutes and then run water through the filter to get rid of the dust particles before installing the filter in your coffee maker. If coffee grounds are showing up in your cup, clean the top and bottom needles of your brewer and run a brew cycle with just water to see if the problem is solved. If the black particles are still collecting in your cup, run a full descale process for your coffee maker.