Some adaptations a plant would need to survive in a water biome would be a waxy surface to control water intake, for plants that float on water, oxygen sacs inside the plant to allow the plant to float, and having a different water circulation system allowing the roots to be for anchorage and not taking in water.
There aren't very many plants that grow in a water biome but here I've listed the four that I've found.
The water lily has a waxy surface allowing a controlled water intake. It also has air sacs that help it float on the water. They also have roots that take in oxygen
Tape grass has narrow leaves without stomata. The roots are also anchored in the ground to help keep them in place
Some adaptations cattails have are air channels that help stay straight and point upwards. They have their seeds stored in the brown bundles at the top of the plant. The seeds spread by wind and will detach to reproduce again.
Algae is a very unique plant because it is submerged completely in water. Most plants wouldn't be able to survive at all but algae has antenna pigments, which are special cells that allow the plant to harvest the suns energy while being in water. They also can vary in color for proteins tirón against their predators.
The product I made based on a water Lily's leaf design is a waterproof and footing iPhone case. I would make it with a water resistant casing and a large pocket filled with air allowing it to float.