The time it takes to freeze a gallon of water varies from minutes to several hours. The time it takes is based on several factors including temperature and the pureness of the water.
The freezing point of water is 32 degrees F, but impurities present in water may lower this temperature further. The temperature of the water when it is placed in the freezer is a factor. Warm water takes longer, while cold water typically takes less time to freeze. The quantity of water is another factor. It takes more time for a gallon of water to freeze than 1 liter of water.