2) Fill the glass with ice, add the light rum and top up the glass with soda water. Stir and garnish with four reserved kumquat slices.
1) Combine the sugar and water in a nonreactive 2L heavy-bottomed saucepan over a medium-high heat and bring to a boil. All the sugar crystals should completely dissolve.
2) Remove from the heat and pour into a clean medium-size bowl. Cool completely before using. Simple syrup can be stored in the refrigerator, indefinitely, if kept in an airtight container.