Humans need freshwater to survive. Freshwater on Earth is distributed unevenly due to climate and weather processes, such as more sunlight being received in the tropics compared to the poles, the Earth's rotation and how it influences circulation in the atmosphere and oceans, and the Earth's topography.
Key learning points
Of all the water on Earth, only 3% is freshwater; the rest is salty
70% of Earth's freshwater is frozen in the cryosphere (polar ice caps, ice sheets and glaciers)
Water vapor in the atmosphere is a small fraction of freshwater on Earth, but is critical for Earth being habitable
Run-off from rain and snow over land is important for replenishing groundwater
Freshwater is critical for agriculture and determines crop and pastureland productivity