In addition to water what would most likely be found in a plant central vacuole

In addition to water, the central vacuole of the cell contains waste products because it serves as the final store for waste products of the cell. It isolates materials which may be harmful to the cell by storing them and thus such materials are contained.

Plants cells often come in contact with foreign materials that they do not need, or have parts that are worn out and no longer useful. If these materials were allowed to float freely in the cytoplasm of the cell, they could damage or cause harm to the plant cells and so they are removed and kept separate in a safe place - the central vacuole.