The tiny black particles at the bottom of the bottle are just activated carbon from the BRITA® filter. Activated carbon particles are made from coconut shells. Like all natural products, coconut shells are subject to natural variation in product quality. Sometimes this leads to abrasive parts of the coal entering your filtered water. It can help to remove the coal dust by treating the filter element as described in the product manual. If customers drink this activated carbon dust, it will not affect their health because it is harmless.