Heat the water in a glass measuring cup in the microwave (or in a small pan on the stove) until almost boiling. Add the sugar and stir to dissolve. Cool slightly, then pour into a blender along with the raspberries and pulse until pureed. Pour the raspberry simple syrup through a fine sieve to strain out the seeds. Refrigerate until cold (can make ahead).
PREPARE THE COCKTAILS:
In a medium pitcher, combine the raspberry simple syrup, 1½ cups water and lemon juice. Divide ice between 4 medium glasses. Divide raspberry lemonade between the glasses. Top each glass with 1 ounce (or more) of the vodka. Stir to combine, and garnish with skewers of raspberry and lemon (or float them in the glass). Serve immediately.