Is there a pile of salt left?
No.
Only some of the water goes through the membrane. The rest of the water becomes saltier and is returned to the ocean.
step five
reverse
osmosis
If a membrane separates salt water and fresh water, fresh water will naturally flow through it to the salty (more concentrated) side. That's called Osmosis. But here, the pressure from the pumps forces water through the membrane to the fresh water side, removing all of the salt and leaving it behind. So it's called Reverse Osmosis.
