In a saucepan over medium heat, stir together 2 cups (500 mL) water, sugar, thyme and ginger. Bring to a gentle boil. Reduce heat to low and simmer, uncovered, for about 15 min. Cool 30 min., then strain syrup into a clean sealable bottle or jar. (To cool syrup more quickly, strain immediately into a measuring cup or bowl and place in the freezer.) Syrup can be made ahead.
Add soda water to a pitcher and stir in the lemon juice. Add 6 tbsp (90 mL) of the syrup to the pitcher. Taste and add more syrup if necessary.
Serve over ice and garnish each serving with a sprig of thyme.
Any leftover syrup will keep in the refrigerator, covered, for up to 2 weeks. To make a single serving of lemonade, stir together 2 tbsp (30 mL) syrup and 2 tbsp (30 mL) lemon juice. Pour over ice into a glass, top with soda water. Optional: Add 1 oz (1 tbsp/15 mL) gin or vodka to each serving.
Chilling Time: 30 min.