Homemade Tonic Water

Bring water and sugar to a boil in a saucepan, stirring until sugar dissolves.

Reduce heat to low; stir in lime zest, lime juice, lemon grass, citric acid, and powdered cinchona bark. Simmer until cinchona is thoroughly dissolved, about 30 minutes.

Remove from heat; let mixture cool, about 15 minutes. Strain through a colander. Run the syrup through coffee filters or cheesecloth to remove sandy bits of bark.