Here's why:

* Heterogeneous mixture: A mixture where the components are not evenly distributed and can be easily separated.

* Soda water is a mixture of carbon dioxide gas dissolved in water.

* Carbon dioxide bubbles are visible and can be separated from the water, making it a heterogeneous mixture.

While it might look like a single substance, the carbon dioxide bubbles are distinct from the water, making it a mixture rather than a solution.