1 - Activated Alumina Fluoride removal filter cartridge. Activated alumina is also widely used to remove fluoride from drinking water. In the US, there are widespread programs to fluoridate drinking water. Activated alumina filters can easily reduce fluoride levels from .5 ppm to less than .1 ppm. The amount of fluoride leached from the water being filtered depends on how long the water is actually touching the alumina filter media. Basically, the more alumina in the filter, the less fluoride will be in the final, filtered water. Lower temperature water, and lower pH water (acidic water) are filtered more effectively too.