A circular polarizing filter is the main tool to reduce water-surface reflections. Reflected light from water is often strongly polarized, so rotating the filter can greatly reduce or even eliminate glare, depending on the angle.

Lighting also matters: try to position or soften your light so it does not bounce directly back from the water surface into the lens. Better light placement can reduce reflections before they become a problem.

For color accuracy, place a known white object in the water beside the subject and make a reference shot using the same setup and lighting. You can then use that frame to correct white balance in post-processing.

A waterproof housing/case may protect gear around water, but it is not the main solution for surface reflections. The most useful combination here is a polarizer plus careful lighting and a white-balance reference.