In a heatproof mug or glass, combine the boiling water, tea bags, and sugar. Stir to dissolve sugar. Allow to steep five minutes, remove tea bag and squeeze into mug to release any liquid. Let mixture cool.

In a cocktail glass or mason jar, gently muddle the nectarine slices and mango using the back of a wooden spoon. Add the ice to the glass. Pour the cooled tea mixture over the ice, add sparkling water and drink immediately.