Density data of the water + carbon dioxide system were determined using a calibrated vibrating tube mass flow meter with a uncertainty below 0.15%. Measurements were performed in the pressure and temperature regimes (1 to 30) MPa and (284 to 332) K, respectively. The water-rich phase density showed a pronounced dependence on pressure and temperature whereas the CO2-rich phase density did not change from the pure density within the measuring uncertainty. A regression function was developed which describes the experimental data in the range studied.