Yes it is dangerous to drink too much water.
Drinking too much water can cause water poisoning because your kidneys cannot flush out the excess water.
We all need water to drink to survive and stay healthy but if you drink gallons of water everyday then you could actually die or have kidney failure instead of helping your kidneys.
Water intoxication or water poisoning occurs when the amount of salt and other electrolytes in your body becomes too diluted.
When that happens it leads to a condition known as hyponatremia which is a condition that causes sodium (salt) levels to become dangerously low.
You usually have to drink more than a gallon of water in a short amount of time before you get water intoxication.
I have drank 1 gallon of water during the day in the summer to stay hydrated and it was never an issue but if you drank 2 gallons of water or more then it could become a problem.