MMWD began fluoridating its water because voters in Marin passed two separate ballot measures in the 1970s indicating they are in favor of fluoridation. MMWD does not have the authority to override a public vote, and therefore does not have the authority to stop fluoridating.
In April 2015, the U.S. Department of Health and Human Services announced a change in the recommendation for the optimal fluoride level in drinking water from a range of 0.7 to 1.2 milligrams per liter to a flat 0.7 mg/L. In response to these new recommendations, MMWD lowered the level of fluoride in its water from 0.9 mg/L to 0.7 mg/L. This new level is equivalent to one drop of fluoride in 18 gallons.