Here's how to figure out how many 16-ounce bottles of water make a gallon:

* There are 128 fluid ounces in a gallon.

* Divide the total ounces in a gallon by the size of each bottle: 128 ounces / 16 ounces/bottle = 8 bottles

So you need 8 16-ounce bottles of water to make a gallon.