Answer:
osmosis
Step-by-step explanation:
The process that was going is osmosis.
Osmosis is the movement of water molecules from regions of high water potential to regions of low water potentials through a selectively permeable membrane.
In this case, the membrane is only permeable to water movement and not ions and water molecules move from the side with pure water (which happens to have higher water potential) to the side with 4% sodium chloride until equilibrium in water potential is established between the two sides.