Wash the oranges well and peel off only the bright orange zest, avoiding the white pith to prevent bitterness.
Place the peels into clean mason jars and pour the alcohol over them until fully covered. Seal tightly.
Store the jars in a cool, dark place for 7–10 days, shaking gently every day or two. The peels will fade while the liquid turns a rich orange.
Strain the infused alcohol through a fine mesh strainer into a clean bowl. Discard the peels.
In a medium saucepan, combine the water and sugar. Heat over medium until the sugar completely dissolves, then let the syrup cool to room temperature.
Slowly stir the cooled syrup into the infused alcohol. The mixture will become slightly cloudy as the orange oils blend with the water.
Taste the orangecello and adjust the sweetness with a little extra syrup if desired.
Pour into clean bottles using a funnel. Seal tightly and let the bottles age for at least 2 weeks before serving.
Chill in the freezer for several hours before serving. The finished liqueur should pour smoothly with a bright citrus aroma.