Solvents, such as water, move towards the low osmotic pressure side of a membrane due to a process called osmosis. Osmosis is the movement of solvent molecules across a semipermeable membrane from an area of lower solute concentration (or higher water concentration) to an area of higher solute concentration (or lower water concentration) until equilibrium is reached.
The direction of solvent movement during osmosis is determined by the relative concentrations of solute particles on either side of the membrane. The solute particles cannot freely pass through the semipermeable membrane, but the solvent molecules can. As a result, the solvent moves in an attempt to equalize the concentration of solute particles on both sides of the membrane.
To understand this, consider two compartments separated by a semipermeable membrane. If one compartment has a higher concentration of solute particles (resulting in a lower concentration of solvent), and the other compartment has a lower concentration of solute particles (higher concentration of solvent), water molecules will move from the compartment with higher water concentration (lower osmotic pressure) to the compartment with lower water concentration (higher osmotic pressure). This movement continues until the concentration of solute particles becomes equal on both sides or until equilibrium is achieved.
In summary, solvent molecules move towards the low osmotic pressure side of a membrane during osmosis because they try to equalize the concentration of solute particles on both sides of the membrane.