<p>Accurate measurement of carbon dioxide (CO₂) in water is essential for environmental monitoring, water quality assessment, and carbon flux estimation. Traditional methods, such as titration and conductivity-based methods, are often limited by high costs, operational complexity, or reliance on chemical reagents. This study proposes a new algorithm based on bubbling for determining free CO₂ concentrations (CO₂ (aq)) in water. By introducing air into water and fitting gas-phase CO₂ dynamics with a nonlinear physical model, the initial CO₂ (aq) concentration can be directly obtained. Experiments with tap water at different temperatures yielded CO₂ (aq) concentrations of 121.38 ± 0.74 μmol/L, 184.50 ± 0.92 μmol/L, and 211.11 ± 0.78 μmol/L. Experiments with saltwater yielded CO₂ (aq) concentrations of 128.46 ± 1.83 μmol/L, 165.15 ± 2.20 μmol/L, and 193.20 ± 1.46 μmol/L. Validation against an independent integration method yielded a minimum relative error of 0.67%, confirming the model’s accuracy and stability. Furthermore, a significant negative correlation was observed between temperature and the equilibrium gas–liquid CO₂ concentration ratio, suggesting that temperature effects require correction in practical applications. In conclusion, this method offers a simple and reliable approach for CO₂ measurement in water, with promising applications in environmental science and engineering.</p>