Hydrology is the science that deals with properties and movement of water town Precipitation: rain, snow, sleet woon)lildho (natulam Surface water runoff or overland flow: seep into the ground and become groundwater and progressing as stream flow min Infiltration the water may enter the subsurface environment or may be returned to the atmosphere through evaporation Infiltrating water first encounters the unsaturated zone, in which the pores (voids) between soil particles contain soil, moisture and air. Water from unsaturated zone may migrate into the saturated zone, or may be held in the form of soil moisture to be returned atmosphere by plant and animal life via evapotranspiration.