Why is most of Earth's fresh water unavailable in lakes and rivers?

In the context of hydrologic sciences, it is a common misconception that fresh water is scarce globally; rather, the vast majority of Earth’s water is either saline or locked in forms that are not readily accessible for human use.12

Most of Earth's water—approximately 96.5 percent—is contained in the oceans and is too saline for drinking or most industrial and agricultural applications. Of the remaining fresh water, the largest portion is not found in rivers or lakes but is stored as ice. Approximately three-quarters of all fresh water is trapped in ice sheets, glaciers, and permanent snow, primarily in Antarctica and Greenland.314

Additionally, a significant volume of fresh water exists as groundwater, which resides in soil and geologic strata below the surface. While rivers and lakes are vital components of the hydrologic cycle, they represent a very small fraction of total surface water—less than 0.01 percent combined—making them minor reservoirs compared to the massive quantities of water held in ice and underground aquifers.35