As the water passes over the positively charged carbon surface, the negative ions of the contaminants are drawn to the surface of the carbon granules. Carbon filters require very little maintenance, and are perhaps the most powerful chemical absorbents known to man. bobble's carbon-based filter removes organic contaminants from regular municipal tap water and meets or exceeds NSF International Standard 42 for chlorine, taste and odor reduction. For best results we recommend changing your filter after 2 months or 40 gallons/150 litres. Filter for use with bobble only. WARNING: Do not use where water is microbiologically unsafe or of unknown quality.