1. Rain falls fresh. Evaporating left everything behind last time round, so what falls is nearly pure water.
2. It crosses rock. Every stream dissolves a very small amount of whatever it runs over. A river is faintly salty and you cannot taste it.
3. It reaches the sea. And stops. This is the end of the line — there is no river out of the ocean.
4. The sun lifts the water. Only the water. Evaporation takes H₂O and leaves every dissolved thing where it was.
5. The salt stays. Round and round for a very long time, with a little more arriving every year and none of it leaving.

Water evaporates; salt does not. A lake with a river flowing out stays fresh. A lake with no way out turns salty, like the Dead Sea.

1. Stir half a teaspoon of salt into a small glass of warm water until it disappears. Look: it is clear.
2. Pour a thin layer onto a saucer.
3. Leave it somewhere warm, like a windowsill.
4. Come back the next day.

Where did the salt on your plate first come from? Follow it back as far as you can.