For the simple syrup, in a small pot, add raspberries, sugar, and water. Bring the mixture to a gentle boil. Cook, stirring occasionally, until the sugar dissolves. Take the mixture off the heat and allow it to come to room-temperature. Strain the mixture through a mesh sieve. If you're not going to use the mixture right away, store in an airtight container and place in the refrigerator until ready to use. The mixture can be made 3 days ahead.