To determine the correct set of statements, we need to analyze each statement individually based on the characteristics of water-pollinated plants and specific examples given:

Statement A: "The flowers of Vallisneria are colourful and produce nectar."

This statement is incorrect. Vallisneria is an example of a water-pollinated (hydrophilous) plant. Unlike insect-pollinated flowers, which are often colorful and produce nectar to attract pollinators, water-pollinated flowers typically lack bright colors and nectar because they do not need to attract insects or other animals. Vallisneria flowers are small and inconspicuous.

Statement B: "The flowers of water lily are not pollinated by water."

This statement is correct. Water lilies are typically pollinated by insects, not by water. The large and colorful flowers of water lilies are adapted to attract insect pollinators, contrasting starkly with the typical features of water-pollinated flowers.

Statement C: "In most of water-pollinated species, the pollen grains are protected from wetting."

This statement is correct. In water-pollinated plants, the pollen grains often have a covering or are structured in a way that prevents them from becoming waterlogged and sinking. This adaptation allows them to float on the water's surface and reach the female parts of other plants.

Statement D: "Pollen grains of some hydrophytes are long and ribbon like."

This statement is correct. In some water-pollinated plants, such as seagrasses (e.g., Zostera), the pollen grains are indeed elongated and ribbon-like, which helps them to be transported more effectively by water currents.

Statement E: "In some hydrophytes, the pollen grains are carried passively inside water."

This statement is also correct. Many hydrophytes have pollen grains that are transported by water currents, rather than being actively carried by animal pollinators or the wind. This passive transport is typical in water-pollinated species.

Based on the analysis, Statements B, C, D, and E are correct, while Statement A is incorrect. Therefore, the correct answer is:

Option D: B, C, D, and E only