In many geological formations, a strata that is impermeable to water is on top of the permeable rock strata. However, if there is an area (even many miles away) where water can seep down to the permeable strata, an underground river can develop to carry the water. For this reason, groundwater can be accessed by drilling water wells in areas with little rain, because the groundwater originated in distant areas with more rainwater. | In many geological formations, a strata that is impermeable to water is on top of the permeable rock strata. However, if there is an area (even many miles away) where water can seep down to the permeable strata, an underground river can develop to carry the water. For this reason, groundwater can be accessed by drilling water wells in areas with little rain, because the groundwater originated in distant areas with more rainwater. |