ABSTRACT THEORETICAL equations which describe the pressures caused by one-dimensional impact of water onto soil surfaces were derived from basic mechanics. The pressures of impact on the soil skeleton and in the soil pores were shown to be functions of the densities and volume fractions of the soil pores and skeleton, a dynamic coupling coefficient, and the compressional wave velocities in the two soil fractions. Theoretical or empirical relationships between the dynamic parameters and soil matric potential, porosity, and degree of saturation were presented, and the total and effective vertical stresses and pore water pressures caused by impact were calculated as a function of those static soil properties. The calculated total vertical stresses were of the order of 0.05 to 0.16 the value for impact on rigid surfaces, and were largely a function of soil matric potential and porosity. The calculated pore water pressures were primarily dependent upon the degree of saturation. At high saturation levels and low matric suctions, calculated pore water pressure exceeded calculated effective vertical stress, indicating a liquified and unstable state for that soil condition. The results will be useful in providing input functions for numerical or analytical studies of soil response to waterdrop impacts.