There are around 3.8 liters in a gallon. So you would need to drink around 2 and half 1.5 liters to equal a gallon.
How Many 1.5 Liters Do I Have To Drink To Equal A Gallon?
1 Gallon is almost 4 liter . So you would have to drink 2 and 2/3 of 1.5 liter bottles .