These germs produce acids that cause decay and leave behind deposits that injure the gums. One of the big defenses against this process is fluoride which builds up the resistance of teeth to these acids by hardening the enamel. In areas where the water is not fluoridated, children's teeth can be substantially protected against cavities by fluoride in drop or tablet form. But do be careful. Too much of a good thing can create other problems.
Excess fluoride can cause staining and mottling of the teeth.
See your dentist to find out if your water is okay.