Not surprising really, as almost everything is hazardous to our health. If you make a rat drink enough water, it will die. This alone is enough evidence for some health nut to preach against the dangers of consuming water. Especially if they know of the Spanish inquisition's habit of torturing people by forcing water down their throats until their stomach burst. Leaving little room for doubt that water consumption can be as injurious to people as rats.
People can also get soggy brains if they drink too much water.
Before glue sniffing became popular it was people sculling water for a cheap high that was the danger. Now it's ecstasy users who need to be careful not to get carried away while following public health warnings about the risks of becoming dehydrated while dancing all night. You might think that if it is not bad for you, then there is no reason to avoid it. But that's not how public health works. Just because water will not kill you, does not mean you should not avoid it.