When two aqueous solutions that differ in solute concentration are placed on either side of a semipermeable membrane and osmosis is allowed to take place, the water will move from the side with lower solute concentration (higher water concentration) to the side with higher solute concentration (lower water concentration). This movement happens because water tends to move down its concentration gradient to equalize the solute concentrations on both sides of the membrane. The side with higher solute concentration exerts greater osmotic pressure and "pulls" water toward it until equilibrium is reached or the osmotic pressure is balanced by hydrostatic pressure.