In this, as with so much else there is a spectrum/scale involved. We need water to function, the question is how much. Too little water intake and we dehydrate and probably there is a level below which we suffer irreparable damage even though we then subsequently get sufficient water to rehydrate. Far too little water and we die.
At the other end we can drink too much water, as with intoxicated people under the influence of the drug "ecstasy" (I think that's the one) and numerous young people have died after drinking water uncontrollably.
In between there is a "neutral" zone whereby no permanent harm is done whether more or less water is consumed, excess water passes through the body, is dumped, but there is a limit to how quickly that happens. Within that zone there are those who believe one should drink a minimum of X litres of water daily, regardless of the conditions the person is living under. Clearly, a person who exerts him/herself a lot loses body water more than a person sitting watching TV all day and all night. The two therefore have a different water replacement job to do. An African tribe (Tuareg ?) is known to survive very hot and dry conditions and they drink far less water than Europeans (and they tut-tut at the waste of good water with all that constant drinking by Westerners) so it seems people can at least to some extent condition themselves to need more or less water yet remain perfectly healthy.
I used to work in places where the temperatures might go up as high as 50 degrees Celsius and there were people working with me who drank far more water than I did. Then and now, being a healthy individual, I leave my body to tell me if I need more liquid - I drink a small glass of water with meals and then I drink additionally whenever I am thirsty. At 72 I am very well and take no medicine of any kind.
Then there is a health supplement and theory grouping which includes those who make money out of promoting "lifestyle" trends and they are very vociferous. Their followers are, at least for a while, also very vocal. I think people should be free to choose sensibly. I choose to drink water when my body tells me I need it rather than letting some health guru (whether medically qualified or not) persuade me to override what my instincts tell me - perceived toxins or no toxins. Others can do what they want and I would not deny them the self satisfaction of being better because they follow a trend.