The aim of this lecture is to present on Ground Water: Concepts. Rain and snowmelt that infiltrate the ground. Soil and rock act as giant sponges, they are full of tiny pores and cracks that are usually less than millimeters in size which allows water to infiltrate and collect underground. Groundwater and surface water are one connected water system. Water wells intercept groundwater that may be on its way to springs that feed streams and rivers.