- dissolve 1tbsp citric acid (or ~4tbsp lemon juice) in some water and freeze in a 1 liter plastic bottle.
- fill almost the rest of the way with water, add 1tbsp baking soda. Cover and thaw in fridge.
Result: You have made club soda. Mild carbonation, and a very slight hint of minerals and salt. Drink straight or flavor as desired.
Optional: Freeze a buffer layer of plain water over the acidified water before step 2 to make sure the ingredients don't react too soon
