The journey begins with water meeting rock

Rainwater picks up carbon dioxide, which forms a weak acid in water. As this water moves across and through the ground, chemical weathering releases dissolved substances from minerals in rocks. Streams and rivers carry some of those substances toward the coast.

The material does not need to look like visible grains of kitchen salt. Much of it travels as ions: electrically charged atoms or groups of atoms dispersed through the water. Clear water can therefore contain dissolved minerals even when nothing appears to be floating in it.

As NOAA explains, land runoff is a major source of the salts found in the ocean. The sea receives the accumulated contributions of drainage systems spread across continents.

Rivers carry salts without usually tasting salty

Calling a river “freshwater” does not mean it contains absolutely no dissolved salts. It means their concentration is relatively low. Rainfall and other freshwater inputs continually replenish many rivers, while flowing water transports dissolved material downstream.

The ocean is a much larger collecting basin. River water delivers both water and dissolved substances, but those two components do not necessarily leave the ocean by the same routes.

Picture a conveyor carrying tiny amounts of material rather than a pipe delivering concentrated brine. Each delivery can be dilute while still contributing dissolved substances to the receiving basin.

This distinction resolves the apparent contradiction: freshwater rivers can supply salts even though their water tastes very different from seawater.

Evaporation takes water into the air and leaves salts behind

At the ocean surface, water molecules escape into the atmosphere as vapor. The dissolved salts do not ordinarily evaporate with them. Removing some water therefore increases the salt concentration in the water remaining behind.

Evaporation does not manufacture salt. It changes the amount of water surrounding salts already present. Rainfall has the opposite immediate effect at the surface: adding freshwater dilutes seawater.

NASA’s ocean salinity explanations describe these exchanges as useful clues to the water cycle. Salinity records the changing balance between freshwater arriving and freshwater leaving.

The ocean also reacts with rocks beneath its floor

Some seawater seeps into cracks in oceanic crust. Near hot rock, it warms and reacts chemically with its surroundings before returning through hydrothermal vents.

Those reactions can add some dissolved substances to the water and remove others. The seafloor is therefore more than a surface beneath the ocean: it participates in the chemistry of the water above it.

The U.S. Geological Survey notes that exchanges between seawater and oceanic rock work in both directions. Describing every vent simply as a salt dispenser misses that balance.

Typical seawater contains about 3.5 percent dissolved salts

A commonly used average is about 35 grams of dissolved salts per kilogram of seawater. In a simplified 1,000-gram sample, that means roughly 35 grams of salts and 965 grams of water.

This is an average, not a universal recipe. The concentration changes from place to place and with depth.

Sodium and chloride are the dominant dissolved ions, but seawater also contains other components. Calling everything in it “table salt” hides that chemical variety.

Different places have different freshwater budgets

Where evaporation is strong relative to freshwater input, surface water tends to become saltier. Near major river mouths or in areas with substantial rainfall, surface water can be less salty. Mixing and currents redistribute those differences.

Sea ice adds another twist. Growing ice excludes much of the salt, increasing salinity in surrounding liquid water. Melting ice adds relatively fresh water instead.

Restricted bodies of water can become especially salty when evaporation removes water faster than freshwater replaces it. The Dead Sea is a familiar example, although it is a lake rather than an ocean.

The Natural History Museum highlights evaporation as a reason some bodies of water become hypersaline. Local water balance helps explain why one average cannot describe every shoreline.

The ocean is not simply getting saltier forever

Rivers keep delivering dissolved substances, but ocean processes also remove them. Some become incorporated into sediments, minerals, or biological material; reactions with the seafloor provide additional exchanges.

NOAA describes modern ocean salt inputs and outputs as approximately balanced. That does not mean every region has constant salinity or that ocean chemistry has remained identical throughout Earth’s history.

It means that an explanation based only on endless accumulation leaves out important pathways. To understand a changing concentration, you need to consider both what enters and what leaves.