The bulk modulus of water is 2.2 x 10^9 Pascals. This number increases as the water comes under more pressure. Another equation for the bulk modulus of water is 2.2. x 10 9 N/m^2, or Newtons per square meter.
The bulk modulus measures the elasticity of a material when it's under pressure on any kind of surface. In the case of water, the intensifying pressure reduces its volume. When the pressure is removed, the water returns to its original volume.
Water's bulk modulus is low because it is relatively easy to compress. The bulk modulus of steel, for example, is orders of magnitude higher than it is for water.