In a blender, combine the cherries and 6 cups (1.2 liters) water (if using frozen cherries, you’ll probably end up with some juice in the bag once they’re thawed; feel free to substitute this for some of the water). Blend on high for 20 to 30 seconds until the mixture is smooth. Strain the juice through a fine-mesh sieve right into an 8-cup (2 liter) measuring cup or pitcher.