In a medium sized pot, combine blueberries, lavender and 4 cups of water. Place on the stove on medium high heat and bring to a boil.
Once the mixture reaches a boil, turn down heat to low and let simmer for 25 minutes.
Add sugar and stir until it dissolves, then strain the syrup through a fine mesh sieve into a mason jar.
Squeeze the lemons and strain the juice and add it to the jar then refrigerate the syrup until it's cold. It's also a good idea to chill your soda water as well.
When ready to serve, place the syrup in a large pitcher and add 4 cups of carbonated water. Serve immediately over ice.
If desired, garnish with fresh lavender sprigs, a slice of lemon and fresh blueberries.
A single recipe makes 72 ounces or about 2 liters of soda.
To make a single glass of soda, the ratio of blueberry syrup to water is 5 parts syrup to 4 parts soda water. For a 6 ounce portion, it's easiest to use metric, so the recipe would be 100ml syrup and 80ml soda water.
This beverage is quite rich and sweet so it doesn't lose it's punch when served over ice. If you'd like to serve it straight you may want to add additional soda water.
I haven't tried it yet, but I think the syrup would be great for snow cones!
Make it ahead! The syrup can be refrigerated up to 3 days or frozen up to a month.