Landscape lighting devices are meant to be outdoors, so if installed correctly and properly maintained they should have no problem with normal rain. However, while they are resistant to water, they are not meant to be submerged underwater. If water gets inside the electrical components that will most likely short the system. Immediately turn off the power to the system and allow it to dry thoroughly before attempting any repairs. Inspect for any damaged components and replace them as needed to prevent further issues. Remove the cause of the flooding (lost covers, broken glass lenses, etc.). If the fixture is in a place with repeated flooding, then that fixture has to be moved to a new location or an underwater fixture can be used in its place.