impurity

Water has to be pushed through a semipermeable membrane that blocks the salt and other impurities from going through.

Sometimes the heroin can be cut with impurities that make people sick.

The acetylene prepared from this substance has a very characteristic odor due to impurities, the chief of these being phosphine.

This sponge will absorb readily the gross impurities of the water, and can easily be taken out and cleaned once or twice a week.