Here's why:

* Osmosis: Osmosis is the movement of water across a semipermeable membrane from a region of high water concentration to a region of low water concentration.

* Hypotonic solution: A hypotonic solution has a lower concentration of solutes (and therefore a higher concentration of water) than the solution it is being compared to.

* Distilled water: Distilled water has virtually no solutes.

Therefore, when distilled water is placed next to a solution with any solutes (like a cell), water will move from the distilled water (high water concentration) into the solution (lower water concentration) to try to equalize the solute concentrations.