📚 Study helper: This page helps you learn and practice for school. Read it, listen to it, and try to answer this: where does the ocean's salt come from, and why don't rivers taste salty?
Ocean water tastes salty.
River water does not taste salty.
But rivers flow into the ocean.
So where did all that salt come from?
The short answer is rain, rocks, and rivers, working very slowly.
NOAA says that long ago, the early seas were probably only slightly salty.
The ocean became saltier over a very long time.
Pick your grade:
Elementary: Rain, Rocks, and Rivers
Salt takes a long trip to get to the ocean.
Here is the trip, step by step.
1. Rain falls on the land
Rain falls to Earth.
Then it runs over the land.
NOAA says this is how the trip starts.
2. Running water breaks up rocks
As rain runs over the land, it breaks up rocks.
The water picks up minerals from the rocks.
The USGS says all natural waters pick up dissolved salts and minerals from touching soils and rocks.
The bits are dissolved in the water, so you cannot see them.
3. Rivers carry the salts to the ocean
Streams and rivers carry the minerals away.
The rivers flow into the ocean.
NOAA says the ocean collects all of the salt and minerals from all of the rivers that flow into it.
4. The ocean keeps the salt
The sun warms the ocean.
Some ocean water turns into water vapor and goes up into the air. The USGS calls this evaporation.
The salt does not go up. The salt stays behind in the ocean.
People use this same trick to make table salt. They let salty water dry up in shallow ponds, and the salt is left behind, the USGS says.
Rain, rocks, and rivers kept doing this for a very long time, so the ocean got saltier and saltier.
So why don't rivers taste salty?
Rivers carry salt too, but only a little bit at a time.
And rain keeps filling rivers and streams with fresh water.
NOAA says that is why rivers and streams don't taste salty.
The river water keeps moving on to the ocean. The ocean is where the salt piles up.
A fun salty place: the Dead Sea
The USGS says the Dead Sea is extremely salty.
Its water is so dense, which means so packed with salt, that people float in it and do not sink, like lying on a mattress.
Middle School: The Full Story, Step by Step
Start with what "salty water" really means.
The USGS says saline water is water that contains significant amounts of dissolved salts. The most common salt is sodium chloride, the same salt you know as table salt.
Scientists measure the salt by weight, in parts per million, or ppm. If water has 10,000 ppm of dissolved salts, then one percent of the weight of the water comes from dissolved salts, the USGS says.
On the USGS scale, fresh water has less than 1,000 ppm. Ocean water contains about 35,000 ppm of salt.
Long ago: only slightly salty seas
NOAA says that in the beginning, the primeval seas were probably only slightly salty.
Over time, as rain fell to the Earth and ran over the land, breaking up rocks and transporting their minerals to the ocean, the ocean has become saltier.
That is NOAA's one-sentence version of the whole story. The steps below unpack it.
Step 1: Water touching rock picks up dissolved solids
The USGS says all natural waters contain some dissolved solids from contact with soils, rocks, and other natural materials.
Dissolved solids are all the substances dissolved in the water added together. Combinations of the dissolved parts, called ions — sodium and chloride, for example — form salts.
Salinity is the word scientists use for how much dissolved salt the water holds.
When water moves through rocks and the minerals dissolve into it, scientists call that wearing-down process weathering.
Step 2: Rivers deliver the load, every year
Streams and rivers carry the dissolved minerals to the ocean, and the ocean collects all of the salt and minerals from all of the rivers that flow into it, NOAA says.
It is a huge delivery. NOAA estimates that rivers around the world carry about four billion tons of dissolved salts to the ocean every year.
Rivers in the United States alone discharge 225 million tons of dissolved solids to the ocean each year, NOAA estimates.
Step 3: Evaporation takes water away and leaves the salt
The USGS says evaporation is the process that changes liquid water to gaseous water, called water vapor. About 90 percent of the moisture in the air came from water evaporating from oceans, seas, lakes, and rivers, and the oceans supply most of it.
Only the water goes up. The dissolved salts stay in the ocean, so what is left behind is saltier.
The USGS gives a clear test of this idea: people make table salt by evaporating saline water in shallow ponds. The water leaves, and the salt remains.
The USGS also says evaporation concentrates dissolved solids in dry places, where there is less water to dilute what weathering sets free.
And the Dead Sea shows the extreme case. It is a lake with no way for water to flow out, the USGS says, so its water leaves mainly by evaporating — and it has extremely high salinity.
Why rivers still taste fresh
Rivers are part of the delivery system, not the storage place.
Rain replenishes freshwater in rivers and streams, so they don't taste salty, NOAA says.
Their dissolved load keeps moving downstream instead of piling up.
The ocean, by contrast, is the end of the line. It stores the water — and the salt — for a very long time.
Is the ocean still getting saltier?
Probably not, NOAA says.
About the same tonnage of salt from ocean water is probably deposited as sediment on the ocean bottom.
So the yearly gains may offset the yearly losses.
In NOAA's words, the ocean today probably has a balanced salt input and output, and so the ocean is no longer getting saltier.
Salt water hides underground, too
The USGS says there is an extensive amount of very salty water in the ground in the western United States.
Rain that soaks down into the ground can meet rocks that contain minerals that dissolve easily, and that turns the water saline.
Groundwater can move for thousands of years, the USGS says, and can become as saline as ocean water.
Words to Know
Saline: Saline water is water with significant amounts of dissolved salts in it. The most common salt is sodium chloride — table salt.
Dissolved: Dissolved means mixed all through the water. The USGS calls everything dissolved in water, added together, the dissolved solids.
Mineral: A mineral is part of what rocks are made of. Rain running over the land breaks up rocks and carries their minerals to the ocean.
Evaporation: Evaporation is the process that changes liquid water to gaseous water, called water vapor. The water goes up into the air. The salt stays behind.
Salinity: Salinity is the amount of dissolved salt in water. The USGS measures it by weight, in parts per million.
Sediment: Sediment is material that settles to the bottom. NOAA says about as much salt is deposited as sediment on the ocean bottom as rivers bring in each year.
📚 Study helper: Great job! Now try this. Say the salt's trip out loud, in order: rain falls and runs over the land, the water breaks up rocks and picks up minerals, rivers carry the salts to the ocean, and evaporation takes water up but leaves the salt behind. Then answer: why don't rivers taste salty? Rain keeps filling them with fresh water.
Sources
NOAA National Ocean Service — Why is the ocean salty, but rivers flowing into it are not?: https://oceanservice.noaa.gov/facts/riversnotsalty.html
USGS Water Science School — Saline Water and Salinity: https://www.usgs.gov/water-science-school/science/saline-water-and-salinity
USGS — Chloride, Salinity, and Dissolved Solids: https://www.usgs.gov/mission-areas/water-resources/science/chloride-salinity-and-dissolved-solids
USGS Water Science School — Evaporation and the Water Cycle: https://www.usgs.gov/water-science-school/science/evaporation-and-water-cycle
USGS Water Science School — Oceans and Seas and the Water Cycle: https://www.usgs.gov/special-topic/water-science-school/science/oceans-and-seas-water-cycle
How these sources were used: The main USGS Saline Water and Salinity page was read in full, but its ocean story is only one short line, so this page was built on the NOAA page above plus the three fuller USGS pages listed here, which were also read in full. The NOAA page is the main source for the rain, rocks, and rivers story. Checked November 2026.