Sparkling mineral waters, like club soda, are great for plants. Plants absorb nutrients best when they are dissolved in water. And sparkling mineral water takes carbon dioxide and a host of other essential macro-nutrients straight to their root systems. In fact, plants that are watered with sparkling mineral water grow faster and greener than plants watered with tap water alone.
Allow the sparkling water to come to room temperature. Refrigerated water will shock your plant's roots and eventually kill it.
Pour the sparkling water from the bottle and into your watering can (or any other receptacle) and let it settle for a minute or two. By transferring the carbonated water, you are allowing it to release some of its carbon dioxide. While the gas is good for plants, an over-abundance of it may change the pH of the soil.
Water the plant as usual. However, avoid getting water on the foliage. In indoor plants especially, this is a great way to encourage mold growth.
Set aside or refrigerate any leftover sparkling water for use next time. Even if it's flat, it's still ideal for your plants.