Freshwater is naturally occurring water on the Earth's surface in bogs, ponds, lakes, rivers and streams, and below-surface in aquifers and underground streams. Freshwater is characterized by having low concentrations of dissolved salts and other total dissolved solids. The term explicitly rejects seawater and brackish water.
The source of almost all freshwater is Precipitation from the atmosphere, in various forms. Freshwater falling as precipitation contains materials dissolved from the atmosphere and material from the sea and land over which the rain bearing clouds have traveled.
In coastal areas, where saltwater is dominate in large bodies of water, freshwater may contain significant concentrations of salts derived from the sea if windy conditions have lifted drops of seawater into the rain-bearing clouds. This can give rise to increased concentrations of sodium, chloride, magnesium and sulfate.
Where freshwater meets salt water is known as an Estuary.
We all depend on freshwater, but alas most of the world's water is salt water. The graphics below shows where most of the water is stored.
- In the first bar, notice how only 2.5% of all Earth's water is freshwater, which is what life needs to survive.
- The middle bar shows the breakdown on that 2.5% which is freshwater. Almost all of it is locked up in ice and in the ground (think of the Himalayas, Greenland and Antarctica.) Only a bit more than 1.2% of all freshwater (which was only 2.5% of all water) is surface water, which serves most of life's needs. That's .03% or 3 our of every 10,000 gallons of water in the wordis fresh water.
- The right side bar shows the breakdown of only the surface freshwater, which was only about 1.2% of all freshwater. Most of surface freshwater is locked up in ice, and another 20.9% is in lakes. Notice the 0.49% of surface freshwater that is in rivers. Sounds like a tiny amount, but rivers are where humans get a large portion of their water from. That is just one gallon out of every million in the world!
Here's another way to think about is: