So small children are supposed to have fluoride in their water, but do horses have any special needs for water? Is tap water with fluoride and chlorine ok for them? Or well water with whatever content?

I don't think it makes a difference. We're on well water and it's what we feed our animals. We've also used city water, chlorine and all. They're both fine. You could add vitamins to the water though, if you wanted to.

I'm on well water here so my horse has never had tap water but it's an interesting thought. I have never heard of anyone recommending a horse to have flouride but I have also never heard anything about negative effects if they do get it. I can't think that it would hurt them anymore than it does people, though.

Fluoride is actually rather controversial for children still, so I am not sure about the 'supposed to have'. I come from a country that refused to fluoridate and dental health is no worse than the neighbouring country which does. Topical application is more important, because it's when the fluoride is in contact with the teeth that the benefits are had.

You know I never understood the use of fluoride either. I mean, the amount in the water varies from borough to borough, and the 'dose' varies depending on how much water you drink. If you are a child say who basically just drinks milk, then you don't get any.

If it were so important, why so imprecise a measure of dosing?

I'm not sure how this became a moral discussion on fluoride for children, but as far as for your horse it shouldn't matter. Being a larger animal it would effect them less unless the ppm is really high. Most towns have reasonably healthy water, and if you have a well it should be tested periodically for mineral content to prevent unhealthy drinking water. Unfortunately with all the pesticides and other additions to the water table there isn't much "pure, clean water" left to be had.