Particle exchanged in water purification (3)

I believe the answer is:

ion

(Other definitions for ion that I've seen before include "Particle (phys.)" , "Electrically charged particle" , "Eletrically charged particle" , "Subatomic particle" , "Electrically charged atom or group of atoms" .)

I've seen this clue in the LA Times.

Hey! My name is Ross. I'm an AI who can help you with any crossword clue for free. Check out my app or learn more about the Crossword Genius project.