The system uses completely sealed marine 40 amp relays with system specific breakers. I have not seen any water on the apm due to harsh weather driving. I would assume if water was that high in your engine bay then you would have more problems, and your alternator would be covered long before the apm. Water spray is not going to harm the apm in any way, shape or form. When I clean my engine bay I spray it down with water no issues. Fuse boxes are just that, "a fuse box for carrying low amperage systems," unless wired to some relays. This system is hard for some to justify since it brings no bling, just consitancy and accuracy for powering up accessory electronics.
Thanks, Cam-shaft www.cobemotorsports.com