This paper proposes a relationship for the physics and mechanics constants of porous media related to water storage rate and ground settlement under a surface load variation condition. This provides the basis for accurate calculation of ground subsidence. Traditional equations for vertical deformation, groundwater flow and land subsidence due to surface loading were developed using Jacob's assumptions. This paper derives a skeletal elastic specific storage rate. The new deformation and flow equations are similar to the traditional ones based on Jacob's assumptions except that the pore-water head in the traditional equations corresponds with the margin between the pore-water head and the water-column height given in the proposed equations representing the surface load. The analysis show that increasing the surface loading leads to land subsidence, rise in pore-water head and decrease in elastic water storage capacity. The maximum subsidence is equivalent to the subsidence triggered by lowering the water head to the equivalent water column height. The maximum rise of the water head is also equal to the equivalent water column height. The maximum water released to a specific volume of porous medium is close to that resulting from reduction in the water head by the equivalent column height.