Compressibility of air and water

A syringe is filled with air and the nozzle is sealed with a finger. Pressing down on the syringe plunger significantly reduces the volume of the trapped air. The same syringe is then filled with water and the experiment is repeated. Now, even with considerable force, the plunger can barely be pushed in.
This direct comparison illustrates the vast difference between the compressibility of gases and liquids. Whilst the molecules in a gas are widely spaced and can be easily compressed as pressure increases, in liquid water they are already packed closely together. Water is therefore virtually incompressible; its minimal change in volume in this experiment is not visible to the naked eye.