The data sheet document for the 400 Series states in its camera cleaning section that water should not be used on the camera lens. Also, on the D415 and D435 models, the grille on the casing would be an obvious means for water to penetrate to the inside. So using the 400 Series unprotected in the wet is likely not a good idea. Apart from that, the cameras otherwise work very well outdoors.
However, RealSense cameras have been used underwater with protective housings. Answers 3 and 4 on the discussion linked to below provide information about using RealSense underwater.