Planet waterless is categorized as a desert world. Can be terraformed to Arid and Island, but not garden... If garden isn't possible, how would island be?
Also, with the new world types (I can terraform from desert to arid, for example) we are really going to need some form of tooltip to let you know what the effects on your population would be from the terraforming... Its REAL easy to overpopulate a world with a terraforming incident...