this ‘danger’ is extremely rare and will only occur if you combine very long instances of exercise with drinking a lot of water without replenishing electrolytes at the same time. The term is ‘hyponatremia’.
If you drink, let’s say, 4 cups of water while you exercise you are not in any danger. But if you decide to drink 4 gallons over a short period of time, you could run the risk of ‘water intoxication’.
Stay well and drink responsibly (even water).
I agree with Karin. It can also be a concern with endurance athletes, but more because they exercise for such a long duration that they sweat out a lot of additional salt and electrolytes that can not be replaced by water alone. For these athletes, salt tabs or a electrolyte replacement drink are often recommended during endurance training.
I thought I might add to Karin’s post.
There are both extremes with drinking too much water or being dehydrated.
Hyponatremia is when there is a decrease concentration of sodium in the blood and hypernatremia is the opposite–an elevated concentration of sodium in the bloodstream.
In hypernatremia water deficits and not salt excesses cause relative sodium levels to rise.
Hope this serves to be insightful.