Depends on how often you'll be having tea in the cabin. Room service is not the fastest thing in the world if you find yourself craving a tea "NOW!" (Although ChucksOk probably gets immediate service on the Seabourn ships as opposed to the ones we commoners travel on.
) But aside from room service, there is always hot water dispensed from the beverage "islands" in the buffet area.
Nothing says you can't bring your own travel kettle, but keep in mind there is typically only the one power outlet in the cabin. If you don't wish to have to pack the kettle, Chucks suggestion of room service would do.
Carnival Cruise Lines:
Fantasy 90, Celebration 95, Victory 05, Conquest 05, Spirit 6/06, Freedom 6/08, Holiday 7/08, Victory 6/09, Valor 9/09, Dream 6/10, Splendor 8/10,Conquest 8/11,Magic 11/11,Triumph 4/12,Spirit 7/12,Freedom 11/12, Triumph 2/13 - The fire cruise, Magic 1/14
NCL Dream October 2006, RCCL Mariner OTS June 2007, Celebrity Silhouette 2013