Answer :
Osmosis causes water to move into the cell. If an animal cell is completely surrounded by fresh water, it will burst because eventually water will fill the entire cell.
Because distilled water has a water potential (ψ) of 0 but the animal cell, its water potential will be much lower causing the distilled water to diffuse into the cell because it wants to be in equilibrium with its surrounding and eventually the cell will 'fill up' and burst in a process called osmotic lysis :)
