Also blending light from the 3rd eye with physical sensation from a variety of points of the body can open the third-eye. It's also a good idea to open and/or check on the other 9 chakras (In 1992 when our Sun changed vibration and we entered the 6th world energetically - the 5th world was the patriarchy two new major chakras began developing - the birth chakra and the thymic chakra). All chakras can be opened together or separately. I often limit how far my chakras are open before I leave my place for my protection and so also not to be assaulted by others' thinking, emotional states etc.

While I resonate with practicing meditation, all manners of higher sound vibrations, eating higher vibrational foods, being open minded and bonding with crystals it's not absolutely necessary to use these methods to develop/heal/open the third eye. Light from the crown chakra, via the optic nerve and interplay of light with other areas of the body that belong with other chakra are invaluable.

Not all tap water contains fluoride - depends on one's locale. Good idea to check first. There are websites. If you're on well water - good idea to check it with a lab if you have the means.