- Most of Earth's water is saltwater found in oceans, while only 3% is freshwater. Of this freshwater, over two-thirds is frozen in glaciers and ice sheets.
- Water is continually cycled through the Earth in the hydrological cycle between oceans, atmosphere, and land via evaporation, condensation, precipitation, and infiltration. This cycle provides freshwater for human and ecosystem uses.
- Groundwater makes up about 96% of unfrozen freshwater and provides 25-40% of the world's drinking water by flowing through aquifers. However, groundwater quality can be impacted by natural and human-caused contaminants.