Juice and zest the blood oranges in a medium saucepan. Some pulp will escape when juicing, and that’s fine. You will strain that situation later. Add the water and sugar and stir until the sugar is mostly dissolved.

Bring to a boil over high heat then reduce to a simmer. Allow the mixture to simmer for about 15 minutes until slightly reduced. Remove from heat and allow steeping for about an hour or so and come to room temperature. Strain the mixture into a glass container with a tight fitting, discarding the solids and store into the refrigerator until ready to use.

To a tall glass add the blood orange syrup. Add ice and top with seltzer. Give it a quick stir and enjoy.