The process thaty causes water to flow into contractile vacuoles?

Answer 1

in fresh water the concentration of solute (particles and ions in water) is lower than that inside the cell. through the process of osmosis, water moves into the cell to equalize the concentration. the water must then be pumped out, so that the cell doesn't burst. in salt water there is less or no difference in solute concentrations inside and outside the cell, and no need to pump water out.

Answer 2

Water flows into contractile vacuoles through osmosis. As the concentration of solutes increases inside the cell, water will flow in to balance the solute concentration. The contractile vacuoles then pump out excess water to maintain the cell's internal environment.