Groundwater exists in these openings in the subsurface environment like water exists within a sponge. Some of it can be removed from the ground and used for things like drinking, watering crops, and in the Columbia Basin, cleaning potatoes in factories before they are made into french fries. Water enters the ground from many sources. In the Mid-Columbia Basin this might include rainfall and melting snow, water from irrigated lawns and farm fields, leakage from rivers high in the mountains, or irrigation canals. If the water from these sources does not evaporate or get used up by plants it seeps into the ground and eventually fills the cracks in the rock or the spaces between the soil particles and becomes groundwater.
Gravity is the main force that makes groundwater move.
Water that seeps into the ground at high elevations is pulled downward by gravity. Because of this, groundwater generally moves downhill toward rivers or lakes at the bottom of valleys. In the Tri-Cities area, rain and snow that falls high on the hills and water put on crops to make them grow seeps into the ground and moves downhill to drain into the Columbia River. The water generally must move through the small spaces between rock particles and through small cracks in rocks, so it travels very slowly. It may take many years for rain that falls this year to become groundwater and then make its way into the Columbia River.