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On Thursday BErney1014 asked for information about fluoride in tap water.

I'm no expert here, but I can provide a little information.  Fluoride is
the common ionic form of the element fluorine.  It stays in the water or
might combine with calcium to precipitate as calcium difluoride (the
mineral fluorite, which is not spelled flourite).  It does not gas out.

The concentration of fluorine in drinking water is regulated.  I *think*
the drinking water limit under US federal guidelines is 1.5 mg/l.  
Fluorine in high concentrations can cause discoloration of the teeth and
abnormal bone growths (fluorosis) in people.  Fluorine levels in excess of
the drinking water standard are fairly common in ground water in the
western US, but instances of fluorosis are rare.

Flouride is important for keeping your tooth enamel strong; so a dentist
might be able to add some more information.  Very small amounts (a few
parts per billion, I think) are commonly added to water supplies for
public health.

I don't think that fluorine is an essential element for plant growth. I
also don't think that at the levels it's regulated for drinking water that
fluorine is toxic to anything, plant or animal.

Roger Miller