Drinking a gallon of water per day may work for some people but could be harmful for others. Although rare, drinking too much water too fast can cause sodium levels in your blood to drop too low, causing a dangerous condition called hyponatremia.
Ultimately, how much water you should drink per day depends on your individual needs. There are many different opinions on how much water you should be drinking every day. Health authorities commonly recommend eight 8-ounce glasses, which equals about 2 liters, or half a gallon. This is called the 8×8 rule and is very easy to remember. I tend to tell patients drink half their weight in fluid ounces. So if you weight 180 lbs drink, 90 fluid ounces of water
While there are general guidelines regarding how much water you should drink, they’re to be used as a rule of thumb.
In most cases, it’s best to trust your thirst — drink when you are thirsty and stop when you are not — and use indicators such as urine color to determine if you’re properly hydrated.