**2. Recharge to discharge**

 What do we mean by *recharge*? It is the water that infiltrates beyond the vadose zone (unsaturated zone) to add to the phreatic zone (zone of saturation); this zone may or may not be an aquifer but part of runoff via interflow and the variable source area that contributes to surface water [2]. Water that *infiltrates* the soil surface does not automatically become groundwater. When plants are present, roots will sequester infiltrated water and pull the water through the plant for physiological needs such as cooling via transpiration. When plants die or go dormant, infiltrated water can move via gravity to the top of the water table or zone of saturation. Temperature can be a factor if water in the vadose zone freezes and becomes immobile until a soil thaw occurs. In the northern hemisphere, the soil thaw occurs in the spring (late March to April). Typically, this is the time of the year water *percolates* through soil pores or fractures to become groundwater. Water that moves in the saturated zone is constrained by the pores (void space) and the pressure or hydraulic head moving groundwater known as *transmission*. The pathway and destination of the groundwater depend on the permeability of the geologic material. Transmissive material is considered an aquifer where water moves relatively quick based on forces of gravity or extraction. Because the earth is not uniform in topography or the size of geologic materials, groundwater will typically move to a *discharge* location over some period. Discharge refers to a point or plane where groundwater is released back to the open free surface. In a natural watershed, these areas of discharge are known as springs, headwater streams, wetlands, ponds, lakes, or even an oasis in the desert [2]. Except for a spring or oasis, it may not be apparent that groundwater is being pushed to the surface. Often, instrumentation is needed to measure groundwater discharge to a surface water body. Yet, where humans have placed a pipe in the ground or water well, discharge occurs through abstraction or pumping for domestic consumption and crop irrigation. The question raised in this chapter is if human interjection in terms of vegetation, land surface management and infrastructure; wells and channel control are changing future sustainability? Human actions have consequences!
