Definitely register that you have a CPAP machine with Royal. (I use the link previously reported, but the email address does work, too.) I would say we have had about 50/50 chance of the distilled water and extension cord in the room when we arrive. We even got an extension cord once while on the Anthem (where it is not needed due to power being available by the beds). We now have two CPAP machines (one each) and bring a multi-plug to power both. During our last cruise, we were able to get a second bottle of water mid-cruise because of using two machines.
As a side-story: One time we did register and when we got to the cabin, they were not there. We reported it to the cabin attendent. We did get the water, but were told there were no spare extension cords available. (Being an older ship, it was needed for the CPAP to reach the bed.) We emphasized the need to the cabin attendent and also reported it to Guest Services. By that evening, two people had delivered extension cords to our cabin. (We thanked and returned the extra / unneeded second set.)
Jim (using Karen's account)