Osmosis, What solution causes a potato to gain more m?!?

Distilled water -has the least amount of solute in it. Putting a potato in distilled water would cause the potato to take in water to try to create a solution of concentration inside the potato close to the concentration of the solution outside. It's the same concept as putting celery in water to make it crunchy (or as it's a plant, it's cells would probably be "turgid")