Not liking the study is one thing but downvoting a link to material without stating a reason is willful ignorance.
At what point does it become dangerous to continue to drink water ?
According to this page [0], the LD50 of water is 6 liters, so somewhere before that.
[0] https://www.compoundchem.com/2014/07/27/lethaldoses/
Well, that's something I never heard about, and contradicts even basic high-school chemistry.
Where did you read it?
https://www.atsdr.cdc.gov/phs/phs.asp?id=210&tid=38
Fluoride is one of those ions that diffuse thought and out of our bodies almost like there is no barrier anywhere.
There is also water intoxication, which can be deadly.