Final answer:
Water moves down its osmotic pressure gradient during osmosis, which is the transport of water through a semipermeable membrane from an area of higher water concentration to an area of lower water concentration.
Step-by-step explanation:
When there is a difference in osmolarity between a cell and its environment, water will move down its osmotic pressure gradient. This process is known as osmosis, which is the movement of water through a semipermeable membrane according to the water's concentration gradient. Osmosis occurs as water moves from an area where it is in higher concentration (and the concentration of solute is low) to an area where its concentration is lower (and the concentration of solute is high), effectively trying to equalize the solute concentrations on both sides of the membrane. The facilitated transport of water by aquaporins may be involved, particularly in biological membranes.