Combine the water and sugar in a saucepan and place over medium-high heat. Whisk until the sugar has dissolved.
Add the raspberry and smash them. Bring to a boil. Reduce the heat and simmer for 20 minutes.
Remove from the heat and strain into an airtight container. Once cooled, cover and store in refrigerator for at least 12 hours and up to 2 weeks.
To make a serving, combine the syrup and ice in a cup. Pour in the club soda and stir.