This is based on the following:

* Density of water: 1 gram per milliliter (g/mL)

* Conversion factors:

* 1 gallon = 3.785 liters

* 1 liter = 1000 milliliters

* 1 pound = 453.592 grams

Therefore, the weight of one gallon of water can be calculated as:

(3.785 L/gallon) * (1000 mL/L) * (1 g/mL) * (1 pound/453.592 g) = 8.34 pounds/gallon