Carbon nanotubes (CNTs) grown on CaCO3 substrate can be easily purified using dilute mineral acids. Here it is shown, for the first time, that as-synthesized CNTs can be purified to a large extent with carbonated water. The amount of CaCO3 that can be dissolved is dependent on the solution volume and the quantity of dissolved CO2. Between 38 and 57 wt % of CaCO3 was removed under atmospheric pressure, and increased to 80 wt % using water pretreated to 3 bar CO2 pressure. CO2 partial pressure was found to have the most significant impact by facilitating the formation of Ca(HCO3)(2). No detrimental effects on CNT quality was determined by Raman spectroscopy and thermogravimetric analysis.