**ANS:**

When you say gallon, be specific: US gallon or imperial gallon.

A 2-liter bottle equals.528344 US gallons or .439938 imperial gallons.

It will take two 2 liter bottles of water to equal 1 gallon of water with an extra .21459 liters of water left over.

It will take three 2 liter bottles of water to equal 1 imperial gallon with an extra 1.454 liters of water left over.