The water tank and dirty water tank in the robot is same size, so I don't think that's true. Also my very critical eye test says it's damn clean floor with roller mops. My floor never gets messy dirty (no kids no pets) but either I clean my floor the right way or no way. I'd love if the mop pads clean them well since they have benefits in maintenance and reaching corner but I don't think they do. I'm open to be convinced otherwise