Blueberry syrup concentrate:

1. Put the water and blueberries in a medium saucepan. Cook over medium heat for about 15 minutes, until the berries have released their juice and the mixture is slightly thickened. 
2. Reduce the heat to low, add the blueberries and let it simmer for about 2-3 minutes, until the sugar completely dissolves.
3. Remove from the heat and strain it through a fine mesh colander over a bowl, pressing the blueberries and gathering as much juice as possible.
4. Let it cool completely before using. Place in the fridge to speed this process up if you want to. 
5. Store the syrup in the refrigerator in an airtight container (preferably glass) if making it in advance.

Blueberry vodka lemonade:

1. Add half the blueberry concentrate and 3/4 of lemon juice with some ice to a large pitcher. 
2. Stir in the cold water and the vodka. 
3. Stir and taste. Add more blueberry syrup, lemon juice or vodka until you reach the desired flavor. You might not use all. 
4. Add lemon slices and stir before serving in tall glasses with ice, lemon slices, fresh blueberries and herbs if you want to.