This is difficult to explain, but it's hypotonic. HypERtonic is where there is where the cells shrivel up because there is more solute (salt is an example of a solute) on the outside, so the water rushes outward towards it and shrivels the cell. Plants like lots of water so they like to be hypotonic, and since you're adding pure H2O, there is no solute being added, so the solute is in the cell, causing the water to rush in. Isotonic is equal throughout the solution.
