In a small saucepan, bring water and sugar to a boil, stirring until sugar is dissolved. Add raspberries; stirring occasionally, until softened, about 2-3 minutes. Remove from heat; let cool completely. Strain through fine-mesh sieve, pressing on solids with back of spoon; discard solids. Transfer syrup to glass jar or airtight container. Store in refrigerator until ready to use. Remaining syrup will keep up to one week.
Fill each glass with ice, 2 tablespoons raspberry syrup, 1½ ounces of vodka, and lemon juice. Stir and finish off with sparkling water or lemon-lime soda.
Garnish each glass with a couple of sprigs of fresh thyme and fresh raspberries.