I was watching a show where an athlete training for an MMA fight had to work very hard to make his weigh-in. In the day or two following he worked very hard at re-hydrating himself, to the extent that he ended up in the hospital from drinking too much water.
YES, drinking too much water can be toxic and kill you it appears.

This is pretty extreme, though, right?
Of course. No one would ever advocate or set up a situation where they would recommend someone drink that much water.

I have read articles where the authors tell of people that have discolored and misshapen teeth from having too much fluoride in their drinking water and diet. The authors usually don’t freely offer up that in the vast majority of these cases the people are living in areas that had water levels several factors higher than anyone would ever recommend introducing into a municipal water supply. Not only was their water over-fluoridated, but so were the chickens, tomatoes, lettuce…in that area as well, compounding the effect.
These fringe articles have been coming up for years.
This past year there was another scare. The UN listed fluoride as a neurotoxin. However, once again not only did they not say what concentrations of fluoride were being researched, critical for proper analysis, but they made absolutely no mention of the possible neurologic effects if one were exposed to the recommended of .7mg/liter.
All of the studies cited were either in areas like China and Colorado that have water (and everything else in that area as a result) that has fluoride levels well in excess of the recommended beneficial titre. The other area of concern cited in theri research was in areas where the fluoride was introduced into water supplies as an industrial waste, certainly polluting the waters with levels way higher than those recommended as well.
Bad journalism and sensationalism.
But, thankfully one of our favorite sites for showing us science in a true light, IFL, has responded to the confusion here:
http://www.iflscience.com/health-and-medicine/largest-survey-yet-finds-fluoridation-safe-and-effective/all/