As much as I like this unit and the amount of scent that it emits, and that it cycles off and on, getting it open/taking the top off to add more water and oils is SUCH a pain in the rear end. And it gets messy, too, since there is still water in the unit while one tries to wrangle to top off, while keeping it level, which doesn't quite work.... There has to be a better design.UPDATE: Rather unexpectedly, I received a call from Innogear, the manufacturer of this unit. The representative noted that other customers had the same issues I did, and she was calling to offer me a replacement in a different size-my choice of a variety-which was shipped to me at lightning speed, free of charge. The new unit is a different design and is SO EASY to use! The lid just lifts off and on. It is much larger than the one I initially bought (100 vs 500ml) and it's nice to have one that lasts so long and has additional features. Really impressed with the replacement but moreso with this company and the care they take in sincerely making customers happy! I will buy from them again.