Why water cannot be compressed?

Answer 1

Not only water, no liquid is compressible. That is the basics of hydraulics, thanks to Pascal. He only discovered that pressure when exerted at one point of a liquid within a container (closed system) it spreads evenly at all area and the whole liquid is evenly pressurized.

Now, compression is possible when only there is intermolecular space is reduced, like in gas. Even solids could be compressed, but only their shape will change.

Compression should make a change in the volume of a substance in given space. And therefore, liquids can not be compressed. (the change could be very very insignificant even after applying huge pressure in terms of Giga Pascals)

Answer 2

Liquid water, for example, transforms to solid ice when cooled to temperatures below 0 °C (32 °F), but ice can also be produced at room temperature by compressing water to pressures roughly 10,000 times above atmospheric pressure.

Answer 3

Water molecules are already packed closely together and have strong intermolecular forces due to hydrogen bonding, which makes them resistant to compression. When pressure is applied, the molecules can rearrange and slide past each other, but ultimately air or other gases trapped in the water will compress rather than the water itself.

Answer 4

Density.