The compressibility of water is a function of pressure and temperature. At 0 °C in the limit of zero pressure the compressibility is 5.1×10-5 bar−1. In the zero pressure limit the compressibility reaches a minimum of 4.4×10-5 bar−1 around 45 °C before increasing again with increasing temperature. As the pressure is increased the compressibility decreases, being 3.9×10-5 bar−1 at 0 °C and 1000 bar. The bulk modulus of water is 2.2×109 Pa.
The low compressibility of non-gases, and of water in particular, leads to them often being assumed as incompressible. The low compressibility of water means that even in the deep oceans at 4000 m depth, where pressures are 4×107 Pa, there is only a 1.8% decrease in volume.
Still that’s 1.8%