Potato cells in distilled water will have difference in concentration (concentration gradient) of water between the extracellular and intracellular environment. In this case, there will be a higher amount of solvent outside relative to inside which means that inward osmosis can occur.
This is the diffusion of water molecules across a membrane, from high to low concentration. Osmosis occurs from areas of high solvent(water) and low solute (dissolved substances) to areas of low solvent and high solute until an equilibrium is reached on both sides of the membrane. The distilled water has a higher concentration of solvent with low solute compared to the inside of the potato cell.
As the distilled water moves into the cells of the potato, their vacuoles will gain the excess solvent and expand. The cell membrane will be pushed against the non-living cell wall and this increases turgor pressure. This will cause the cells to expand which will be seen with a light microscope. The potatoes will look thicker and more plump due to the influx of water. If the mass of the potato before and after the experiment is measured by weighing it, the potato will weigh more after inward osmosis occurs.