One of the most common uses for activated carbon is treating water. It acts as a sort of buffer, removing harmful toxins from wastewater, groundwater and drinking water. It even improves taste and odor.
It cleans the air you breathe, too: PAC is often built into air purifiers to adsorb volatile chemicals. (A note on adsorb vs. absorb: the latter indicates that one substance fully mixes with another; adsorb refers to two substances that bind together on a superficial level.)