The prominent intracellular plant organelle that contains mostly water is the vacuole.

Here's why:

* Large and Central: Vacuoles are large, fluid-filled sacs that occupy a significant portion of a plant cell's volume.

* Water Storage: They primarily store water, which contributes to cell turgor pressure, providing structural support and rigidity to the plant.

* Other Functions: Vacuoles also store various substances like pigments, nutrients, and waste products.

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