Hydrating is good and water is essential to our body so drinking more is good, right? Actually not really. in fact too much hydration can cause death. In fact, there were at least 14 people who died because of over hydration in the present.
Overhydration or drinking too much water causes our kidneys to become unable to excrete excess water. These excess water causes sodium to become diluted and this creates swelling of the cells, which is actually, as you can guess, be really bad. This condition is called exercise-associated hyponatremia (from hypo, meaning less or lacking, and natrium which is the Latin name of sodium).
In the mild cases, overhydration may cause dizziness, nausea, and puffiness. but severe cases may lead to coma, seizures, confusion, and as said before death.
So when should you hydrate? The Medical News Today article published in 2015 recommends drinking only when you are thirsty. This avoids dehydration and overhydration at the same time. Though dehydration is more frequent, overhydration is just as dangerous.
Always having water readily available so you can have a drink when you're thirsty is enough to prevent dehydration.
So 8 glasses a day? Not really. There is really no recommended water consumption per day. It depends and varies per person. Also, there is water in most of the food we eat and that counts as a method of rehydration too, thou in small amounts.
So don't force yourself in drinking too much water, even if you're an athlete or physically active.
I know you don't trust me much but you can read the online article published by the Medical News Today here: https://www.medicalnewstoday.com/articles/296081.php