A literal ton wouldn’t do anything measurable but yeah, adding more material of lower atomic numbers would in theory work considering it’s a fusion engine and wouldn’t exactly scoff at having to break the water molecule before using it.
Edit: like maybe if there was a star with a bunch of particularly wet planets around it and you somehow deorbited them, since as far as I’m aware the elements heavier than iron are just dead weight, they wouldn’t put out the star or anything.