Half a lemon juice + 1 liter of sparkling water = ça mousse (foam)
You can also add slices of fresh ginger roots and add them to this drink. You can also make variations to this recipe: it works with oranges, strawberries, grapefruits or anything you like.
The Guardian – Grandma’s all-natural recipes: when life gives you lemons, preserve them: https://www.theguardian.com/lifeandstyle/2017/apr/30/grandmas-all-natural-recipes-when-life-gives-you-lemons-preserve-them

Ginger and Lemon sparkling water.

You can also squeeze the juice of the half lemon directly into the glass of sparkling water.
Opt for glass containers, as plastics contain endocrine disruptors.