Recipe note: Serve freshly mixed; keep juice refrigerated before mixing.
Keep the glass measures separate
Mix the two juices first, then divide the ice among all four glasses. Each receives a measured juice-base amount and the same measured sparkling-water amount. That division makes the four-serving yield clearer than pouring by eye until the first two glasses look full. Use suitable larger glasses if your chosen ice leaves too little carrying room.
Keep the sparkling water chilled and sealed until the glasses are ready. Add it gently, give the short stir, and finish with one orange slice each. The stated liquid yield excludes ice, so it is not a promise that a small cup can hold the whole serving. Serve freshly mixed as directed; leave another round’s base and sparkling water separate until needed.
Timing and servings are estimates. Equipment, ingredients and portion sizes affect the result.