That is 0.0000007% fluoride.
The added (or natural) fluoride in drinking water becomes part of your tooth enamel.
Not just by bathing your teeth with fluoride, but also by entering the cells that nourish a healthy tooth.
Fluoride is an enzyme or adjuvant that enhances the production of new tooth enamel, which is how your teeth respond to normal wear and tear and prevent cavities.
So, this very small amount of fluoride, an ion of fluorine, goes to your teeth and nowhere else?