Put the blueberries into a saucepan and pour in enough water to cover the fruit. The blueberries should bob back up to the top of the water. Heat to boiling.
Mash the blueberries with a wooden spoon. Keep the fruit in the water while mashing, but turn off the heat.
Bring the blueberry mash just to the boiling point again and remove it from the heat.
Pour the mashed berries and water into a colander that is placed over a bowl, large jar or other receptacle. Use the wooden spoon to press the juice out of any berries that might have stayed whole during the first mashing process.
Taste the blueberry juice concentrate you have created and add sweetener to taste. Granulated sugar, honey or artificial sweeteners take the bite out of the tartness of the fruit.
Add water to the blueberry juice concentrate. Generally, a mixture of 3 to 4 parts water to 1 part concentrated juice renders a beverage that is of a clear, thin consistency. Add less water for a thicker, smoothie-like drink and more potent blueberry flavor or more liquid for a flavored-water type beverage.
Store your homemade blueberry juice in a covered jar or container in the refrigerator.