Water is the most active component in all geological systems. It has an important effect on the physical properties of minerals and melts. It also plays a key role in the evolution of the Earth. Accurate thermodynamics data on water are currently confined to pressures below 1.0 GPa and temperatures below 900°C. Presented in this paper are new data available on theP-T properties of water at pressures up to 5.0 GPa, developed from differential thermal analysis and ultrasonic wave amplitude analysis. It has been found that there may exist another ternary point at 3.0 GPa and that ultrasonic wave amplitude change of ice-water transition shows two inflection points above 2.0 GPa, consistent with the two peaks of differential thermal curves above 2.0 GPa. It may be a new phenomenon which needs further study.