Oceans are salty because runoff transports minerals and salts from the surface. When ocean evaporates from heat, salt remains in the ocean and water rises.
Even though rain water washes minerals and salts into rivers and lakes, they are mostly freshwater. This is because their minerals get washed away and transported to an outlet at the nearest ocean.
So unlike salty oceans, lakes and rivers constantly have the minerals washed away.
How much total volume is salt water?
Imagine you’re stranded on a raft in the middle of the ocean. You see nothing but open water. But none of it is fresh water to drink. If you compare salt water and freshwater:
SALT WATER: about 97.2% is not suitable for drinking because it has salt in it.
FRESH WATER: If we sum up all the sources of freshwater, about 2.8% of water on Earth is freshwater.
The majority of salt water is from the 5 oceans that surround continents. And the average depth of oceans is 2.7 kilometers so water volume is about 1,338,000,000 cubic kilometers.
Oceans are foundation of water cycle. Water moves continuously in nature in three stages: evaporation, condensation and surface runoff.
Ocean currents are like giant conveyor belts moving huge amounts of water all the time. While wind drives surface ocean currents from the Coriolis effect, temperature and salt gradients mostly influence deep ocean currents.
What is the distribution of fresh and salt water?
Earth is unique because of how much water it stores. But the distribution of total volume of water differs disproportionately for fresh and salt water.
If you crunch the numbers, Earth holds about 326 million trillion gallons (326,000,000,000,000,000,000 gallons) of water. Already mentioned, most of the water is salt water. Just a small portion of it is fresh water.
Here’s the percentage and total (in gallons) for the global water distribution of all sources of water.
|Streams, wetlands and swamps||3,260,000,000,000,000||0.001%|