Divide the cucumber, radish, potato, egg, scallion, and dill between each of 4 shallow soup bowls. Sprinkle ¼ teaspoon of flaky sea salt on the vegetables in each bowl.
Gently stir together the kefir and mineral water in a pitcher. (Don’t over-mix or you’ll lose all the bubbles.)
Pour 1 cup of the kefir mixture into each bowl, and add 1 ice cube to each. Serve immediately.
