Water can be classified as hard or soft, depending on the presence of certain salts of calcium and magnesium. When water contains high concentrations of carbonates and bicarbonates of calcium and magnesium, we term the hardness of water as temporary hardness. Presence of chlorides and sulphates of calcium and magnesium cause the water to be termed as containing permanent hardness. Soft water, on the other hand, contains low concentrations of these salts. It is difficult to produce lather from soap, when using hard water.
In the process of distillation, we remove all the microbes and minerals present in the water. Since no minerals or salts are present in the distilled water, it is soft water.
Carbonated water has effervescence in it due to addition of carbon dioxide (also known as carbonation). Bottled water is generally carbonated and sold in the market. Bottled water is soft and the process of carbonation does not make it hard. Hence, we can say that carbonated water is soft.