https://help.kobo.com/hc/en-us/artic...-Kobo-eReaders
Waterproof your Kobo Aura H2O (Model number N250 only)
If you have a Kobo Aura H2O with a port cover on the bottom, keep the port cover firmly closed to prevent water from entering the Micro USB port and Micro SD slots.
That's possibly to protect the SD card